Wireless and mobile technologies for the Future Internet
Bokor, László
Simon, Vilmos
Szabó, Csaba A.
Wireless and mobile technologies for the Future Internet
írta Bokor, László, Simon, Vilmos, és Szabó, Csaba A.
Publication date 2015
Szerzői jog © 2015 Bokor László, Simon Vilmos, Szabó Csaba A.
Tartalom
Wireless and mobile technologies for the Future Internet ... 1
1. 1 INTRODUCTION TO WIRELESS AND MOBILE COMMUNICATIONS ... 1
1.1. Contents ... 1
1.2. SHORT HISTORY OF RADIO COMMUNICATIONS ... 1
1.3. Research and first demonstrations ... 1
1.4. The birth and development of radio ... 2
1.5. Mobile telephony, main milestones ... 2
1.6. BASIC CONCEPTS ... 2
1.7. Electromagnetic spectrum: "lower" part ... 2
1.8. Electromagnetic spectrum: "upper" part ... 3
1.9. Radio, microwave, infrared, etc.? ... 4
1.10. Electromagnetic waves: frequency, wavelength, energy (1) ... 4
1.11. Electromagnetic waves: frequency, wavelength, energy (2) ... 5
1.12. The electromagnetic spectrum ... 5
1.13. Radio waves? ... 5
1.14. Frequency management ... 6
1.15. Wireless communications? ... 6
1.16. Opportunities and challenges ... 6
1.17. Opportunities and challenges ... 7
1.18. EXAMPLES ... 7
1.19. Terrestrial microwave links ... 7
1.20. A VSAT network ... 8
1.21. Cellular mobile network ... 9
1.22. GSM cellular mobile network ... 9
1.23. WLAN ... 10
1.24. Wireless sensor network ... 10
1.25. Sensor network on/in a body ... 11
1.26. Structure of the course ... 12
2. 2 WIRELESS COMMUNICATIONS: BASIC CONCEPTS ... 13
2.1. Contents ... 13
2.2. 1 PROPAGATION AND ANTENNAS ... 13
2.3. Physical phenomena affecting the propagation of radio waves ... 13
2.4. Frequency bands and their propagation characteristics ... 13
2.5. Surface propagation (flat waves) ... 14
2.6. Ionospherical propagation (space waves) ... 14
2.7. Direct (line-of-sight) propagation ... 15
2.8. Line-of-sight (LOS) and non-line-of-sight (NLOS) communications ... 15
2.9. Propagation in free space ... 16
2.10. Propagation in free space (cont.) ... 16
2.11. Reflection, two way propagation witn a reflected wave from the Earth surface .. 16
2.12. Diffraction ... 17
2.13. Knife-edge diffraction ... 17
2.14. Diffraction, Fresnel zones, diffraction attenuation ... 18
2.15. Fresnel-zones ... 18
2.16. Fresnel zone ... 19
2.17. Defining line-of-sight propagation based on Fresnel zones ... 20
2.18. Multipath propagation ... 20
2.19. Propagation in the satellite communication channel ... 21
2.20. 2 NOISES AND INTERFERENCES IN RADIO CHANNELS ... 21
2.21. Noises and interferences in wireless channels - overview ... 21
2.22. 3 MODULATION TECHNIQUES ... 21
2.23. What is modulation and why doing it? ... 21
2.24. Modulation, digital modulation ... 22
2.25. ASK - Amplitude Shift Keying ... 22
2.26. The spectrum of the ASK signal: illustration by a sinusoidal modulating signal . 22 2.27. Spectrum of the ASK signal ... 23
2.28. ASK: advantages and disadvantages ... 23
2.29. FSK - Frequency Shift Keying ... 23
2.30. FSK: advantages and disadvantages ... 24
2.31. GMSK ... 24
2.32. (Binary) PSK in the time and frequency domain ... 24
2.33. Bit error probability for ASK, FSK and PSK ... 25
2.34. Multi-level PSK: QPSK (Quadrature PSK) ... 26
2.35. The constellation diagram ... 27
2.36. QPSK constellation diagram ... 27
2.37. 8PSK ... 28
2.38. BPSK-QPSK-8PSK ... 29
2.39. Bir error rates for binary and multi-level PSK modulations ... 29
2.40. QAM - quadrature amplitude modulation ... 29
2.41. QAM constellation diagram ... 30
2.42. Adaptive modulation ... 30
2.43. "Analog" modulation ... 30
2.44. 4 SHARING A COMMON RADIO CHANNEL: MULTIPLEXING ... 31
2.45. Multiplexing: FDM and TDM ... 31
2.46. TDM - time division multiplexing ... 31
2.47. Wavelength division multiplexing ... 31
2.48. CDM - code division multiplexing ... 31
2.49. Principle of code division multiplexing ... 32
2.50. Principle of CDM, example ... 32
2.51. CDMA: advantages and disadvantages ... 33
2.52. 5 SHARING A COMMON RADIO CHANNEL: MULTIPLE ACCESS ... 33
2.53. Multiplexing multiple access ... 33
2.54. Ways to divide a common channel ("fixed" methods) ... 33
2.55. Example of a common radio channel: using a satellite repeater ... 34
2.56. Random access (random = free) ... 34
2.57. The simple Aloha protocol ... 34
2.58. "Slotted" Aloha ... 35
2.59. Reservation Aloha ... 35
2.60. Applications of the Aloha protocol ... 35
2.61. Carrier Sensing Multiple Access ... 36
2.62. Performance of carrier sensing multiple access ... 36
2.63. Centralized multiple access methods ... 36
2.64. Roll-call polling ... 37
2.65. Probing ... 37
2.66. Reservation ... 38
2.67. Reservation: dividing the channel ... 39
2.68. 6 NETWORKING ASPECTS IN WIRELESS COMMUNICATIONS ... 39
2.69. Network topologies ... 39
2.70. Centralized topologies ... 39
2.71. Centralized topologies: advantages and disadvantages ... 40
2.72. Decentralized topologies ... 40
2.73. Fully connected network: advantages and disadvantages ... 40
2.74. Multi-hop peer-to-peer network: advantages and disadvantages ... 41
2.75. Broadcast networks ... 41
2.76. Literature ... 41
3. 3 WIRELESS LOCAL AND METROPOLITAN AREA NETWORKS ... 41
3.1. Contents ... 41
3.2. BWA- BROADBAND WIRELESS ACCESS: WLAN, WMAN ... 42
3.3. Family of wireless network technologies according to coverage area ... 42
3.4. WLANs and WMANs: coverage and data rates ... 42
3.5. Our objectives ... 42
3.6. WIRELESS LANS - IEEE 802.11 ... 43
3.7. Wireless LANs? ... 43
3.8. WLAN devices ... 44
3.9. 802.11 standards ... 44
3.10. Channels (2.4 GHz band) ... 45
3.11. Physical layer technologies for wireless communications ... 45
3.12. 802.11 sub-standards corresponding to different physical layer technologies ... 45
3.13. DSSS: detection, noise protection ... 46
3.14. Frequency Hopping Spread Spectrum (FHSS) ... 46
3.15. FHSS: main parameters ... 46
3.16. OFDM ... 47
3.17. Channel allocation ... 47
3.18. OFDM: advantages and disadvantages ... 48
3.19. WLAN: main operating modes ... 48
3.20. WLAN topology (BSS and ESS) ... 48
3.21. Wireless Access Point (WAP) - Bridge ... 49
3.22. 802.11 frame format ... 49
3.23. Frame control field ... 49
3.24. 802.11 addresses ... 50
3.25. 802.11 MAC layer - access methods ... 50
3.26. Distributed Coordination Function (DCF) ... 50
3.27. SIFS-PIFS-DIFS ... 51
3.28. DCF algorithm ... 51
3.29. CSMA/CA (DCF) ... 51
3.30. Exponential backoff algorithm ... 52
3.31. Problem of the "hidden" station ... 52
3.32. Solution: RTS/CTS handshaking ... 52
3.33. Network Allocation Vector (NAV) ... 53
3.34. RTS/CTS + NAV: solution to the hidden station problem ... 53
3.35. Busy channel ... 54
3.36. Evaluation of RTS/CTS ... 54
3.37. Point Coordination Function (PCF) ... 54
3.38. PCF operation ... 55
3.39. DCF PCF ... 55
3.40. Quality of Service (QoS) assurance in WLANs: the 802.11e standard ... 55
3.41. WLAN theoretical and measured performance ... 56
3.42. Mesh networks based on WLAN- devices: the 802.11s standard ... 56
3.43. Mesh networks based on WLAN- devices: the 802.11s standard ... 57
3.44. Too many nodes to reach the backbone: access capacity goes down ... 57
3.45. Dual-radio mesh (IEEE802.11b/g/n for access, IEEE802.11a for backhaul) ... 57
3.46. Multi-radio mesh (IEEE802.11b/g/n for access, IEEE802.11a for backhaul) ... 58
3.47. Very high speed WLANs: the 802.11n standard ... 58
3.48. Security in WLANs ... 59
3.49. WIMAX - IEEE 802.16 ... 59
3.50. WMAN and WiMAX ... 60
3.51. WMAN - WiMAX ... 60
3.52. WIMAX application areas ... 61
3.53. WIMAX application areas: "hot zone" ... 61
3.54. Example of a city backbone: Trento, Italy ... 61
3.55. LOS - NLOS environment ... 62
3.56. WiMAX standards, versions ... 63
3.57. MAC ... 63
3.58. TDD - FDD ... 64
3.59. Frequency bands ... 64
3.60. Protocol structure, MAC layer ... 65
3.61. MAC common part sublayer ... 65
3.62. Traffic parameters (1) ... 66
3.63. Traffic parameters (2) ... 66
3.64. WiMAX applications and QoS ... 66
3.65. Traffic classes (1) ... 67
3.66. Traffic classes (2) ... 67
3.67. QoS classes and parameters ... 68
3.68. Wi-Fi - WiMAX comparison ... 68
3.69. Design example: combined use of Wi-Fi mesh and WiMAX ... 68
3.70. WiMAX summary ... 69
3.71. The future of WiMAX? ... 69
4. 4 Lecture 6 Mobility management ... 70
4.1. Content ... 70
4.2. Introduction ... 70
4.3. Challenge ... 70
4.4. Terminal mobility ... 70
4.5. Network mobility ... 71
4.6. Problems of mobility 1/2 ... 71
4.7. Problems of mobility 2/2 ... 72
4.8. Example: routing and mobility ... 72
4.9. Other issues of mobile use cases ... 72
4.10. Mobility support ... 73
4.11. Mobility management ... 73
4.12. Location Management ... 74
4.13. Paging ... 74
4.14. Handover ... 74
4.15. Convergence: All IP paradigm ... 75
4.16. Problems of IP handovers 1/2 ... 75
4.17. Problems of IP handovers 2/2 ... 75
4.18. Inter-cell handovers ... 76
4.19. Applying domains in the network ... 76
4.20. Micro-mobility ... 76
4.21. Micro-mobility protocols ... 77
4.22. Grouping of micro-mobility schemes ... 77
4.23. Another grouping of micro-mobility schemes ... 77
4.24. Planning of micro-mobility domains ... 78
4.25. Optimal size of Location Areas ... 78
4.26. In which layer to handle mobility? ... 78
4.27. Mobility management at the OSI layers ... 78
5. 5 MOBILITY MANAGEMENT IN THE NETWORK, TRANSPORT AND APPLICATION LAYERS ... 78
5.1. Contents ... 78
5.2. IP unifies network architectures ... 79
5.3. Symbiosis of different technologies ... 79
5.4. The need for vertical handovers ... 80
5.5. Network layer mobility management 1/2 ... 80
5.6. Network layer mobility management 2/2 ... 81
5.7. Main mobility scenarios ... 81
5.8. IPv6 for mobility management ... 82
5.9. The Mobil IPv6 protocol family ... 83
5.10. Mobile IPv6 ... 83
5.11. NEMO Basic Support protocol ... 84
5.12. Operation of NEMO Basic Support ... 84
5.13. NEMO BS in practice 1/3 ... 84
5.14. NEMO BS in practice 2/3 ... 85
5.15. NEMO BS in practice 3/3 ... 86
5.16. Multihoming in NEMO networks ... 87
5.17. MCoA (Multiple Care-of Addresses Registration) ... 88
5.18. Flow Bindings ... 89
5.19. Hierarchical Mobile IPv6 (HMIPv6) ... 89
5.20. Dual-Stack Mobile IPv6 (DSMIPv6) ... 90
5.21. Proxy Mobile IPv6 (PMIPv6) ... 91
5.22. Mobility management within the transport layer: Introduction ... 92
5.23. Transport layer mobility management 1/3 ... 92
5.24. Transport layer mobility management 2/3 ... 92
5.25. Transport layer mobility management 3/3 ... 93
5.26. TCP in wireless environments 1/5 ... 93
5.27. TCP in wireless environments 2/5 ... 93
5.28. TCP in wireless environments 3/5 ... 94
5.29. TCP in wireless environments 4/5 ... 94
5.30. TCP in wireless environments 5/5 ... 95
5.31. Indirect TCP (I-TCP) ... 95
5.32. Indirect TCP (I-TCP) ... 95
5.33. Snoop TCP ... 96
5.34. Snoop TCP ... 96
5.35. Snoop TCP ... 96
5.36. Mobile TCP (M-TCP) ... 97
5.37. Fast retransmit/fast recovery ... 97
5.38. Transmission/time-out freezing ... 98
5.39. SCTP ... 98
5.40. SCTP basics ... 99
5.41. SCTP header structure 1/2 ... 99
5.42. SCTP header structure 2/2 ... 100
5.43. SCTP connection setup ... 101
5.44. SCTP data transmission ... 102
5.45. Multistreaming 1/2 ... 102
5.46. Multistreaming 2/2 ... 103
5.47. Multihoming ... 104
5.48. UDP/TCP/SCTP comparison ... 105
5.49. Mobile SCTP (mSCTP) ... 105
5.50. mSCTP handover ... 106
5.51. mSCTP/MIPv6: connection setup ... 106
5.52. IPv6 WLAN/3G multihoming with SCTP ... 107
5.53. Mobility managmenet within the application layer: SIP ... 108
5.54. SIP architecture ... 108
5.55. Proxy Server - 1 ... 109
5.56. SIP transaction, dialog ... 109
5.57. Invitation ... 109
5.58. SIP-based multimedia connections ... 110
5.59. SIP Mobility Support ... 110
5.60. SIP Mobility ... 111
5.61. Mobile IP Communications ... 111
5.62. Mobility management: MIP,SIP,SCTP ... 112
6. 6 WEDGE LAYER AND CROSS LAYER MOBILITY MANAGEMENT SOLUTIONS 112 6.1. Content ... 112
6.2. The Internet infrastructure today ... 112
6.3. The main problem: semantically overloaded IP addresses ... 113
6.4. What could be the solution? ... 113
6.5. Locator-Identifier Split techniques ... 114
6.6. Why HIP? ... 114
6.7. The "position" of the HIP protocol ... 114
6.8. Host Identity Protocol ... 115
6.9. The new namespace ... 116
6.10. Host Identifier ... 116
6.11. Computation of a Host Identity Tag ... 117
6.12. Connection between representations ... 117
6.13. The new layer in TCP/IP ... 118
6.14. IPsec basics ... 118
6.15. IPsec Transport mode ... 119
6.16. IPsec Tunnel mode ... 119
6.17. IPsec BEET mode ... 120
6.18. HIP in operation ... 120
6.19. HIP handshake: Base Exchange (BEX) ... 120
6.20. Initiating the BEX : I1 ... 121
6.21. Starting Session State Setup: R1 ... 121
6.22. Second Initiator Packet: I2 ... 122
6.23. Conclusion of BEX: R2 ... 122
6.24. Other Control Packets of HIP I. ... 122
6.25. Other Control Packets of HIP II. ... 123
6.26. HIP packet format I. ... 123
6.27. HIP packet format II. ... 124
6.28. HIP state machine ... 124
6.29. HIP Security ... 125
6.30. HIP name resolution ... 126
6.31. HIP service discovery ... 127
6.32. HIP mobility and multi-homing ... 127
6.33. Rendezvous server (RVS) ... 128
6.34. RVS registration mechanism ... 129
6.35. HIP DNS example with RVS ... 129
6.36. A complete HIP registration procedure ... 129
6.37. HIP-based micro-mobility: Basics ... 130
6.38. HIP-based micro-mobility: Init. ... 130
6.39. HIP-based micro-mobility: Paging ... 131
6.40. HIP vs. microHIP ... 132
6.41. HIP-NEMO: Basics ... 133
6.42. HIP-NEMO: Connection establishment ... 134
6.43. HIP-NEMO: Nested scenario ... 134
6.44. HIP-NEMO: Handover management ... 134
6.45. HIP vs. MIPv6/NEMO ... 135
6.46. Cross layer optimization: In a nutshell ... 136
6.47. FMIPv6: motivation and basics ... 136
6.48. FMPv6: terminology and entities ... 137
6.49. FMIPv6: predictive handover ... 137
6.50. FMIPv6: reactive handover ... 137
6.51. FMIPv6: packet forwarding scheme ... 138
6.52. Further optimization possibilities ... 138
6.53. GPS-aided predictive mobility management: System model ... 138
6.54. MCoA handover ... 139
6.55. Predictive MCoA handover ... 139
6.56. NEMO BS vs. NEMO MCoA vs. Predictive NEMO MCoA ... 139
7. 7 DISTRIBUTED AND DYNAMIC MOBILITY MANAGEMENT ... 140
7.1. Contents ... 140
7.2. Introduction ... 141
7.3. Mobile internet traffic evolution ... 141
7.4. Scalability problems of mobile internet ... 142
7.5. A solution in nutshell: distributed and flat architectures ... 143
7.6. Evolution of 3GPP/3GPP2 mobile network ... 143
7.7. Steps towards flat networks: LIPA ... 144
7.8. Steps towards flat networks: SIPTO ... 145
7.9. Steps towards flat networks: IFOM ... 145
7.10. Evolution of the 3GPP/3GPP2 PS domain ... 146
7.11. "Ultra flat" architectures in a nutshell: Requirements ... 146
7.12. "Ultra flat" architectures in a nutshell: System design ... 147
7.13. Distributed and dynamic mobility management: Motivations ... 147
7.14. Problem statement: concept of DMM ... 148
7.15. Problem statement: Routing ... 148
7.16. Problem statement: Non-Optimal for Flat Architectures ... 149
7.17. Problem statement: Scalability ... 149
7.18. Problem statement: Signaling Overhead ... 149
7.19. Problem statement: Dynamic Mobility ... 150
7.20. Problem statement: Integration if Different Mobile IP protocols ... 150
7.21. Problem statement: Single Point of Failure ... 150
7.22. Distributed and dynamic mobility management: Scenarios ... 151
7.23. Core-level distribution ... 152
7.24. Access-level distribution ... 152
7.25. Host-level distribution ... 153
7.26. Network based DMM ... 153
7.27. Client based DMM ... 154
7.28. DMM in Wi-Fi networks ... 154
7.29. Distributed and dynamic mobility management: DMM in 3GPP ... 155
7.30. Roots: IPv6 based mobility ... 156
7.31. Hierarchical Mobile IPv6 ... 158
7.32. Proxy Mobile IPv6 (PMIPv6) ... 158
7.33. Function decoupling in current mobility solutions ... 159
7.34. Function reconfiguration for DMM scenarios ... 160
7.35. An example DMM architecture ... 160
7.36. MIPv6 Routing Optimization (RFC 6275) ... 161
7.37. MIPv6 Enhanced RO (RFC 4866) ... 162
7.38. FAMA (draft-bernardos-mext-dmm-cmip-00) ... 163
7.39. D-PMIPv6: Architecture ... 164
7.40. D-PMIPv6: RO and HO management ... 165
7.41. Some example simulation results - Topology ... 166
7.42. Some example simulation results - Handover latency ... 166
7.43. Some example simulation results - UDP PL ... 167
7.44. Some example simulation results - TCP throughput ... 168
7.45. Some example simulation results - VoIP MOS (ITU-T G.107) ... 169
7.46. Conclusions ... 170
8. 8 WIRELESS SENSOR NETWORKS ... 171
8.1. Contents ... 171
8.2. WSN: INTRODUCTION ... 171
8.3. Sensors? ... 171
8.4. Platforms for sensor nodes ... 171
8.5. Sensor network? WSN? ... 173
8.6. MANETs vs WSNs ... 173
8.7. Applications of sensor networks ... 174
8.8. An example: sensor network on/in a body ... 174
8.9. Requirements and challenges ... 175
8.10. New protocols are needed ... 176
8.11. Protocol architecture ... 176
8.12. MAC - Specific circumstances in WSNs*) ... 176
8.13. MAC - Protocols ... 177
8.14. Example: S-MAC - Sensor-MAC ... 177
8.15. Routing *) ... 177
8.16. Classification of routing protocols ... 177
8.17. 1. LEACH - Low Energy Adaptive Clustering Hierarchy ... 178
8.18. 1. LEACH (2) ... 178
8.19. 2. PEGASIS Power-Efficient Gathering in Sensor Information Systems (1) ... 178
8.20. 2. PEGASIS (2) ... 179
8.21. 3. TEEN - Threshold sensitive Energy Efficient Sensor Network ... 179
8.22. 4. APTEEN - Adaptive periodic ... ... 179
8.23. 5. SPIN - Sensor Protocol for Information via Negotiation (1) ... 180
8.24. 5 - SPIN (2) ... 180
8.25. 6. DD - Directed Diffusion (1) ... 180
8.26. 6 - DD (2) ... 181
8.27. 7. MCF - Minimum Cost Forwarding ... 181
8.28. 8 - TTDD - Two-Tier Data Dissemination ... 181
8.29. 9. RW - Random Walks ... 181
8.30. 10. RR - Rumor Routing ... 182
8.31. Localization*) ... 182
8.32. Multi-lateration (ML) ... 183
8.33. Other methods ... 183
8.34. Sensor management *) ... 184
8.35. QoS metrics example ... 184
8.36. Sensor management: topology control ... 184
8.37. References and literature (1) ... 185
8.38. References and literature (2) ... 185
8.39. References and literature (3) ... 185
9. 9 Mobile ad hoc networks ... 186
9.1. Content ... 186
9.2. Network topologies ... 186
9.3. Centralized topology ... 186
9.4. Advantages of centralized topology ... 187
9.5. Disadvantages of centralized topology ... 187
9.6. Decentralized topologies ... 187
9.7. Fully-connected peer-to-peer network ... 187
9.8. Multi-hop peer-to-peer ... 188
9.9. Types of networks ... 188
9.10. Mobile ad hoc networks (MANETs) ... 188
9.11. MANETs ... 189
9.12. "Routing" in MANETs ... 189
9.13. Issues in MANETs ... 189
9.14. Issues in MANETs ... 190
9.15. MAC protocols for MANETs ... 190
9.16. MANET MAC: Channel separation ... 190
9.17. Single channel ... 191
9.18. Multiple channels ... 191
9.19. Multiple channels (cont.) ... 191
9.20. MANET topologies: Flat ... 192
9.21. MANET topologies: Clustered ... 192
9.22. Reducing energy consumption ... 192
9.23. Reducing energy consumption (cont.) ... 193
9.24. Reducing energy consumption (cont.) ... 193
9.25. Reducing energy consumption (cont.) ... 193
9.26. Transmission Initiation ... 194
9.27. Routing in MANETs ... 194
9.28. Conventional routing protocols for MANETs? ... 194
9.29. Conventional routing protocols for MANETs? ... 195
9.30. Routing protocols for MANETs ... 195
9.31. Route discovery ... 195
9.32. Route discovery (cont.) ... 195
9.33. Route maintenance ... 196
9.34. Proactive vs. Reactive Routing ... 196
9.35. Proactive Routing Protocols ... 196
9.36. Destination-sequenced distance-vector ... 197
9.37. Destination-sequenced distance-vector ... 197
9.38. Clusterhead Gateway Switch Routing ... 197
9.39. Clusterhead Gateway Switch Routing ... 198
9.40. Reactive Routing Protocols ... 198
9.41. Ad-hoc on-demand distance vector ... 198
9.42. Ad-hoc on-demand distance vector (cont) ... 199
9.43. Dynamic Source Routing ... 199
9.44. Dynamic Source Routing (cont.) ... 199
9.45. Comparison of Protocols ... 200
9.46. Current Research in Routing for MANETs ... 200
9.47. Wireless sensor networks (WSNs) ... 200
9.48. WSNs ... 201
9.49. MANETs vs. WSNs ... 201
10. 10 LECTURE 12 HANDOVER ENHANCEMENT TECHNIQUES ... 202
10.1. Contents ... 202
10.2. Background: Heterogeneous access networks ... 202
10.3. Reminder: Handover types ... 202
10.4. Handover enhancement in general ... 203
10.5. Handover enhancement in general (cont'd) ... 203
10.6. Scope of IEEE 802.21 MIH ... 204
10.7. Goals of IEEE 802.21 ... 204
10.8. IEEE 802.21 overview ... 204
10.9. 802.21 general architecture ... 206
10.10. 802.21 reference model ... 207
10.11. 802.21 event, command and information services flow mode ... 208
10.12. 802.21 components in detail ... 208
10.13. MIH Protocol Frame Format ... 208
10.14. 802.21 based intertechnology handover example ... 209
10.15. 3GPP ANDSF: Motivation ... 210
10.16. 3GPP ANDSF: Goals ... 210
10.17. ANDSF and OMA-DM ... 211
10.18. Representation of ANDSF information ... 211
10.19. ANDSF in the 3GPP architecture ... 211
10.20. Heterogeneous Handover using ANDSF Information ... 212
10.21. 802.21 and ANDSF ... 213
10.22. A possible ANDSF - 802.21 integration ... 213
11. 11 QUALITY OF SERVICE IN IP NETWORKS ... 214
11.1. Contents ... 214
11.2. Multimedia applications ... 214
11.3. What is QoS? ... 215
11.4. What is the main challenge in IP-based networks? ... 215
11.5. Main approaches to ensuring QoS ... 215
11.6. Traffic descriptors ... 216
11.7. Some tools used in QoS assurance methods ... 216
11.8. An earlier (non-IP) example: ATM - Asynchronous Transfer Mode ... 216
11.9. QoS: where are we? ... 217
11.10. Integrated Services (IntServ) ... 217
11.11. Requirements of applications and the corresponding IntServ services (1) ... 218
11.12. Requirements of applications and the corresponding IntServ services (2) ... 218
11.13. Mechanisms used in IntServ (1) ... 218
11.14. Flowspec: specification of the packet flow ... 218
11.15. Traffic description and policing ... 219
11.16. Token Bucket (TB) in IntServ ... 219
11.17. Admission control ... 220
11.18. Signalling - the RSVP ... 220
11.19. RSVP: how the reservation takes place ... 220
11.20. RSVP - how it works ... 221
11.21. RSVP - "path": in one trsmtsr one rcvr case ... 221
11.22. RSVP - "reservation": in one trsmtsr one rcvr case ... 221
11.23. RSVP - handling a fault ... 222
11.24. RSVP: one trsmtr multiple rcvrs ... 222
11.25. RSVP: multiple trsmtrs multiple rcvrs ... 222
11.26. Handling of packets in IntServ ... 223
11.27. Filterspec: qualification of packets ... 223
11.28. On the scalability of IntServ ... 223
11.29. DIFFERENTIATED SERVICES (DIFFSERV) ... 224
11.30. The main idea of DiffServ (1) ... 224
11.31. The main idea of DiffServ (2) ... 224
11.32. How DiffServ works ... 224
11.33. Marking packet in the edge router ... 225
11.34. Marking, classification and "conditioning" ... 225
11.35. DiffServ - "behavior" of nodes ... 226
11.36. Placing of "DiffServ Code Points" (DSCPs) ... 226
11.37. DiffServ - expedited forwarding (EF) ... 227
11.38. DiffServ - assured forwarding (AF) ... 227
11.39. Assured forwarding (AF) sub-classes ... 227
11.40. DiffServ - advantages and problems ... 228
11.41. IntServ and DiffServ: comparison ... 228
11.42. DiffServ and IntServ: IntServ service in a DiffServ network ... 228
11.43. DiffServ and IntServ (cont.) ... 229
11.44. Summary ... 229
12. 12 QUALITY OF SERVICE IN WIRELESS AND MOBILE NETWORKS ... 229
12.1. Content ... 229
12.2. Reminder: QoS support in a nutshell ... 230
12.3. QoS in wireless/mobile scenarios ... 230
12.4. QoS in the physical layer ... 231
12.5. QoS in the MAC layer ... 231
12.6. QoS in the network layer ... 231
12.7. Application layer QoS ... 232
12.8. Special requirement: adaptive, renegotiable QoS support ... 232
12.9. Most popular QoS techniques ... 232
12.10. QoS techniques for Mobile IP ... 232
12.11. QoS techniques for Mobile IP (cont'd) ... 233
12.12. RSVP problems in MIP scenarios ... 233
12.13. Solution: RSVP over IP Tunnels ... 233
12.14. RSVP Signalling example ... 233
12.15. RSVP in mobile environments ... 234
12.16. Overall Architecture for RSVP in mobile environments ... 234
12.17. Overall Architecture for RSVP in mobile environments (cont'd) ... 235
12.18. Overall Architecture for RSVP in mobile environments (cont'd) ... 235
12.19. RSVP issues in case of IP micro-mobility ... 236
12.20. RSVT issues in case or IP micro-mobility (cont'd) ... 236
12.21. UMTS bearer service ... 236
12.22. UMTS bearer concept for QoS treatment ... 237
12.23. Default and dedicated bearer ... 238
12.24. EPS QoS parameters vs. 3G QoS parameters ... 238
12.25. Standardized QCI characteristics ... 239
12.26. Policy and charging control architecture (3GPP TS 23.203) ... 239
12.27. End-to-end QoS for IP service ... 240
13. 13 FLAT AND ULTRA FLAT ARCHITECTURES ... 241
13.1. Contents ... 241
13.2. Scalability Problems in Future 3GPP Networks for IP-based Services ... 241
13.3. Traffic explosion in the PS domain ... 242
13.4. The LTE/EPC reference architecture ... 243
13.5. Requirements of future architectures ... 244
13.6. Ultra Flat Architecture ... 244
13.7. UFA: an end-to-end convergent fixed mobile network ... 245
13.8. The Ultra Flat Architecture ... 245
13.9. User plane in UFA ... 245
13.10. UFA Gateway description ... 246
13.11. IEEE 802.21 in a nutshell ... 246
13.12. IEEE 802.21 over UFA ... 247
13.13. UFA: General system design ... 247
13.14. In detail: SIP based scenario for UFA ... 248
13.15. In detail: PMIP based scenario for UFA ... 249
13.16. In detail: HIP based scenario for UFA ... 249
13.17. Why HIP: possible roles of HIP in EPC ... 250
13.18. Introducing HIP in 3GPP-access networks ... 251
13.19. Distribution of network functions ... 251
13.20. First phase of HIP-UFA deployment ... 251
13.21. Level of distribution: Centralized ... 251
13.22. Level of distribution: Distributed ... 252
13.23. Level of distribution: Flat ... 252
13.24. Second phase of HIP-UFA deployment ... 253
13.25. Level of distribution: Centralized ... 253
13.26. Level of distribution: Distributed ... 253
13.27. Level of distribution: Flat ... 254
13.28. Inter PGW mobility in EPC Release 10 ... 254
13.29. Ideas ... 255
13.30. Delegation-based HIP mobility service in distributed/flat architectures ... 255
13.31. Traffic forwarding ... 256
13.32. Motivations for "hop-by-hop" traffic forwarding ... 256
13.33. Registration to HIP delegation services ... 256
13.34. Type 1 Delegation Service and CXTP ... 257
13.35. Details ... 257
13.36. Type 2 Delegation Service ... 257
13.37. Details ... 258
13.38. Inter-GW mobility using 802.21 and HIP delegation services ... 258
13.39. HIP handover preparation ... 259
13.40. Handover preparation procedure on HIP layer ... 259
13.41. Handover preparation procedure on HIP layer (cont'd) ... 260
13.42. IEEE 802.21 MIH Commit phase ... 260
13.43. Handover completion phase ... 261
13.44. Performance evaluation of HIP Delegation based mobility services I. ... 261
13.45. Performance evaluation of HIP Delegation based mobility services II. ... 262
13.46. Performance evaluation of HIP Delegation based mobility services III. ... 262
Wireless and mobile technologies for the Future Internet
1. 1 INTRODUCTION TO WIRELESS AND MOBILE COMMUNICATIONS
1.1. Contents
• Short history of radio communications
• Basic concepts
• Electromagnetic and radio waves
• The openness of the wireless channel, advantages, disadvantages, challenges
• Examples of wireless and mobile communications systems
• A mobile cellular network
• Wireless LAN
• Television broadcasting network
• Terrestrial microwave links
• VSAT network
• Wireless sensor networks
• Structure of the course
1.2. SHORT HISTORY OF RADIO COMMUNICATIONS
1.3. Research and first demonstrations
• Scientists whose research results made the invention of radio transmission possible:
• 1867 - Maxwell predicts existence of EM waves
• 1887 - Hertz proves existence of EM waves; first spark transmitter generates a spark in a receiver several meters away
• 1890 - Branly develops "coherer" for detecting radio waves
• First demonstrations of wireless transmission
• 1896 - Guglielmo Marconi demonstrates wireless telegraph to English telegraph office
• 1898 - Nikola Tesla demonstrates a radio controlled boat
• 1897 - Alexander Popov demonstrates transmission of radio waves between different campus buildings in St. Petersburg
1.4. The birth and development of radio
• Who invented the radio?
• All of the above
• Common opinion: Marconi
• Marconi patented his inventions, Popov did not (Tesla did some, and there was a long "patent war"
between him and Marconi)
• Marconi received a Nobel Prize in 1909
• Marconi put radio into commercial use
• Transoceanic Communication
• 1901 - Marconi successfully transmits radio signal across the Atlantic Ocean from Cornwall to Newfoundland
• 1902 - First bidirectional communication across Atlantic
• Voice over Radio
• 1914 - First voice over radio transmission
• 1920s - Mobile receivers installed in police cars in Detroit
• 1935 - Frequency modulation (FM) demonstrated by Armstrong
• 1940s - Penetration of FM radio
1.5. Mobile telephony, main milestones
• 1946 - First interconnection of mobile users to public switched telephone network (PSTN)
• 1960s - Improved Mobile Telephone Service (IMTS) introduced in the USA; supports full-duplex
• 1976 - Bell Mobile Phone has 543 pay customers using 12 channels in the New York City area; waiting list is 3700 people; service is poor due to blocking
• 1979 - NTT/Japan deploys first cellular communication system
• 1989 - Groupe Spécial Mobile defines European digital cellular standard - GSM - deployed in US in 1994
• 2000s - 3 , 4 generation cellular system standards, Bluetooth, Wi-Fi
1.6. BASIC CONCEPTS
1.7. Electromagnetic spectrum: "lower" part
Source: NASA Goddard Space Flight Center
http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html
1.8. Electromagnetic spectrum: "upper" part
1.9. Radio, microwave, infrared, etc.?
• Are they different in principle?
• NO, all of them are electromagnetic waves
• What are electromagnetic waves?
• Photons travelling in a wavelike way, carrying energy, at a speed of light ( meters per second)
• Are they different still?
• YES, they are.
• Different ways and characteristics of propagation in the space
• Different ways of producing and receiving them
• Consequently, different areas of use
1.10. Electromagnetic waves: frequency, wavelength, energy (1)
Electromagnetic waves are characterized by
• frequency, f, [Hz],
• wavelength, , [m],
• energy carried by the photons, E, [eV].
1.11. Electromagnetic waves: frequency, wavelength, energy (2)
• Frequency and wavelength: one of them is enough since f=c/ , c= meters per sec, the speed of light, then why two?
• Why do we need also energy to characterize an e. m. wave?
• Only for practical reason: to avoid large numbers...
• In the radio range, frequency is usually used, since the numbers are quite convenient, e.g. 87.5 MHz for a FM radio channel. Sometimes also wavelenghts, e.g. a frequency of 1 GHz corresponds to 30 cm. Traditional names of some frequency bands also refer to wavelengths, long waves, short waves.
• In the range of the visible light, frequency values are too big numbers, so using wavelenghts is more convenient.
• Ultraviolet, X-ray: frequencies are too high, wavelengths are too tiny, so scientists use energy of photons.
E.g., photons in ultraviolet rays have energy levels of several eV to 100 eV.
1.12. The electromagnetic spectrum
1.13. Radio waves?
• Part of the electromagnetic spectrum between the ultrasound band and the domain of the visible light
• Very wide and not fully utilized band: from kHz to THz (terahertz: Hz)
• Propagation in free space
• Electrical signals are converted into electromagnetic waves and vice versa by transmitter and receiver antennas
• For efficient radiation and reception, antenna sizes should be in the order of the wavelength
• Main antenna parameter: antenna gain
• definition: , where the "effective area" of the antenna, defined by its physical characteristics.
1.14. Frequency management
• "Openness" of the radio channel: distribution of the frequency bands among users is critical.
• Licensed and license-free bands
• In general: licenses should be obtained, exemptions:
• ISM (Industrial, Scientific, Medical) bands
• GHz, GHz
• Regulations:
• global, by the International Radio ...
• regional, e.g. EU directives
• National, e.g. FCC in the US, OFCOM in UK, ...
1.15. Wireless communications?
Simplest scheme: a point-to-point simplex communications:
• Antenna transmits electromagnetic wave
• Wave travels through space
• Power is reduced as wave travels
• Bounces off objects, propagates along parallel paths
• Signal is exposed to environmental effects such as weather
• Channel has noise (natural, industrial)
• Interference by other radio signals is present in the channel
• Distortion of the signal occurs due to limited bandwidth
• Receiver antenna captures wave
• Receiver does its best to extract information from the weak, noisy, interference-prone signal at the highest possible quality, at:
• Minimal BER - bit error rate (for digital signals)
• Minimal mean square error (for analogue signals)
1.16. Opportunities and challenges
• Provides mobility
• A user can send or receive a message no matter where he or she is located
• Added convenience/reduced cost
• Enables communication without installing an expensive infrastructure
• Can easily set-up temporary LAN
• Disaster situation
• Office move
• Developing nations utilize cellular telephony rather than laying twisted-pair wires to each home
• Only use resources when sending or receiving a signal
1.17. Opportunities and challenges
• Noisy, time-varying channel
• BER varies by orders of magnitude
• Environmental conditions affect transmission
• Shared medium
• Other users create interference
• Must develop ways to share the channel
• Bandwidth is limited
• FCC determines how spectrum is allocated
• ISM band for unlicensed use (902-928 MHz, 2.4-2.5 GHz and 5.725-5.875 GHz
• Requires intelligent signal processing and communications to make efficient use of limited bandwidth in error-prone environment
1.18. EXAMPLES
1.19. Terrestrial microwave links
1.20. A VSAT network
From: http://www.acumenquest.com/vsat.html
1.21. Cellular mobile network
1.22. GSM cellular mobile network
1.23. WLAN
1.24. Wireless sensor network
http://www.ece.ncsu.edu/netwis/Design_Optimization.php
1.25. Sensor network on/in a body
1.26. Structure of the course
1. Bevezetés a vezetéknélküli és mobil hálózatok világába 2. Wireless communications: basic concepts
3. Wireless personal area networks
4. Wireless local and metropolitan area networks 5. Evolution of mobile cellular networks 6. Mobility management
7. Mobility management in the network, transport and application layers 8. Wedge-layer and cross-layer mobility management solutions
9. Distributed and dynamic mobility management 10. Wireless sensor networks
11. Mobile ad hoc networks
12. Hálózatváltást segítő technikák 13. Quality of Service in IP networks
14. Quality of Service in wireless and mobile networks 15. Flat and ultra flat architectures
2. 2 WIRELESS COMMUNICATIONS: BASIC CONCEPTS
2.1. Contents
1. Propagation and antennas
2. Noises and interferences in radio channels 3. Modulation techniques
4. Sharing a common radio channel: multiplexing 5. Sharing a common radio channel: multiple access 6. Networking aspects in wireless communications
2.2. 1 PROPAGATION AND ANTENNAS
2.3. Physical phenomena affecting the propagation of radio waves
• Free space attenuation
• Inversely proportional to the distance squared (see later)
• Reflection
• From any surface or medium that can cause reflections in a given frequency band (reflection property is frequency-dependent)
• Examples: buildings in the cm wavelength range or the atmosphere in the range of tens of meters
• Refraction
• Diffraction
• Scattering
• In a medium that contains particles corresponding to a given wavelength, such as in the troposphere
2.4. Frequency bands and their propagation characteristics
• Interesting: propagation characteristics differ by frequency/wavelength decades
• Examples:
• Very long waves (wavelength in the order of km): propagation for very large distances due to diffraction
• Short waves (wavelength in the order of 10 m): surface and reflected wave, reflection from the ionosphere, propagation over large distances, even global coverage is possible
• Microwaves (cm-waves): straight line propagation
2.5. Surface propagation (flat waves)
2.6. Ionospherical propagation (space waves)
2.7. Direct (line-of-sight) propagation
2.8. Line-of-sight (LOS) and non-line-of-sight (NLOS) communications
Metropolitan environment:
reflections from building, shielding effect of buildings
Rural environment:
attenuation due to natural objects such as trees Non-line-of-sight communications:
no direct path exists, utilization only of reflected waves
2.9. Propagation in free space
Received power for propagation in free space (Friis formula):
• , where:
• = transmitter power, ,
• = transmitter antenna gain, dimensionless
• = receiver antenna gain, dimensionless
• = wavelength,
• = speed of light,
• = frequency,
• = system loss, , dimensionless
• = distance between transmitter and receiver,
2.10. Propagation in free space (cont.)
• Another parameter: EIRP (effective isotropic radiated power):
•
• ERP: related to the half/wave dipole antenna, which has a gain of 2,15 dB, therefore
• ERP (in dB) = EIRP (in dB) - 2,15 dB
• Free space loss:
• PL(db)=
• Usually measure in decibels (why?)!
2.11. Reflection, two way propagation witn a reflected wave from
the Earth surface
2.12. Diffraction
Huyghens principle:
2.13. Knife-edge diffraction
2.14. Diffraction, Fresnel zones, diffraction attenuation
• Complicated calculations,
• Simple, practical approach
2.15. Fresnel-zones
2.16. Fresnel zone
r: radius of Fresnel zone [m]
D: distance [km]
f: frequency [GHz]
2.17. Defining line-of-sight propagation based on Fresnel zones
2.18. Multipath propagation
• Signals propagating along different paths arrive at transmitter with different delays, receiver processes the sum of all signals
• Old phenomenon: fading in the short wave radio reception
• How to cope with multipath propagation: multiple transmission and reception:
• method called diversity
• multiple antennas and receivers, optimal combination of signals - space diversity
• Transmission and reception on multiple frequencies at the same time - frequency diversity
• There are different fading models
2.19. Propagation in the satellite communication channel
• Received signal strength is predominantly defined by the free space loss
• Antenna gain of the transmitter and receiver antennas can improve conditions
• Antennas are "directed"
• Antenna gain: ratio of the power density in the main radiating direction to the power density of an isotropic radiator
• Noise conditions are predominantly defined by the thermal noise at the input of the receiver, noises form the radio channel are minor components (cosmic noise because it is small, industrial noise because it can be avoided by proper placing the earth stations)
• For geo-stationary satellites, it is straightforward to calculate the received signal-to-noise ration taking into account the aforementioned components.
2.20. 2 NOISES AND INTERFERENCES IN RADIO CHANNELS
2.21. Noises and interferences in wireless channels - overview
• "Openness" of wireless channels
• Noises
• Thermal noise at the input of the receiver
• Atmospheric noise
• Cosmic noise, galactic noise
• Interferences
• Industrial and other man-made noises
• Interferences from other radio systems
• Often a combination of these factors
2.22. 3 MODULATION TECHNIQUES
2.23. What is modulation and why doing it?
• We need to transmit signals carrying analog or digital information, e.g.
• an FM broadcast signal band limited to 15 kHz,
• A binary or m-ary pulse sequence representing digital data of data rates in the kbps and Mbps range.
• These signals, called "baseband" signals, occupy a frequency band from Hz to an upper frequency defined by the data rate and the coding method.
• Baseband signals cannot be transmitted over wireless channels as they are, why:
• It would require enormous power or extremely large size antennas,
• For a particular wireless communication system, only a specific frequency band can be used, so baseband signals need to be "placed" there.
• Modulation: modifying a parameter, such as amplitude or phase, of a (mostly sinusoidal) carrier wave according to the magnitude of the baseband signal
2.24. Modulation, digital modulation
• "Modulation": using a high frequency (usually sinusoidal) carrier signal to transmit a symbol sequence.
• One of the paramaters of the carrier is being modified according to the symbols, such as
• amplitude: ASK (amplitude-shift-keying),
• frequency: FSK (frequency-shift-keying),
• phase: PSK (phase-shift-keying).
• As a result, the spectrum of the signal to be transmitted is being shifted from the "baseband" to the band around the carrier frequency.
2.25. ASK - Amplitude Shift Keying
2.26. The spectrum of the ASK signal: illustration by a sinusoidal
modulating signal
2.27. Spectrum of the ASK signal
2.28. ASK: advantages and disadvantages
Advantages:
• Modulation and demodulation is simple and inexpensive Disadvantages:
• Linear modulation, sensitive to noises and multipath propagation
• In practice:
• Mainly in optical communications
2.29. FSK - Frequency Shift Keying
Symbol "0" - carrier frequency of , symbol "1 - carrier frequency of
(digital frequency modulation: modifying the frequency of the carrier according to the baseband signal)
2.30. FSK: advantages and disadvantages
Advantages:
• Simple generation and demodulation
• Insensitive to the non-linear distortion, can use efficient amplifiers ...
• which can result to lower power consumption of receivers Disadvantages:
• Bandwidth utilization is not as good as of PSK
• Popular variant:
• GMSK - Gaussian Minimum Shift Keying: used in GSM mobile cellular systems
2.31. GMSK
• Phase changes in a continuous way, no sharp changes
• +: better spectral properties
• +: lower power consumption
• -: more complex processing
• Signal goes through a Gaussian filter before the modulator
• Spectrum: smaller sidebands, lower level of interference between neighboring channels
2.32. (Binary) PSK in the time and frequency domain
2.33. Bit error probability for ASK, FSK and PSK
2.34. Multi-level PSK: QPSK (Quadrature PSK)
2.35. The constellation diagram
• Constellation diagram: symbol is represented by a complex number
• Quadrature modulation: a sinusoidal and a cosinosoidal carrier is modulated by the real and imaginary part of the signal, and both are transmitted on the same frequency
• Receiver decides for the symbol that has a minimum euclidean distance from the received symbol.
• False decision: decision for a wrong constellation point because it is "nearer" due to the added noise
2.36. QPSK constellation diagram
2.37. 8PSK
2.38. BPSK-QPSK-8PSK
• QPSK doubles the BPSK data rate
• But signal-to-noise ratio is lower, or, higher transmitting power is needed for the same SNR
• BPSK: hibatűrő, de alacsony adatsebesség
• 8PSK, 16PSK, ...: increased data rate but BER is also increasing
• See the following diagram for an exact comparison
2.39. Bir error rates for binary and multi-level PSK modulations
• For more than 8-ary PSK BER is too high!
2.40. QAM - quadrature amplitude modulation
• Two carriers, phase-shifted by 90 degrees, are amplitude-modulated and their sum is transmitted
• Result is like a simultaneous amplitude and phase modulation of a single carrier
• Frequently used variants are 16-QAM, 64-QAM, 128-QAM and 256-QAM
• Increasing data rates, but together with increasing BER!
2.41. QAM constellation diagram
Example: 16QAM
2.42. Adaptive modulation
• Changing modulation mode depending on the conditions in the radio channel:
• Interferences from other radio transmitters, change of received signal strength, signal-to-noise ratio etc.
• Transmitter uses information measured in the channel
• Example:
• Channel is noisy: QPSK
• Less noisy channel: 16QAM
2.43. "Analog" modulation
• Modulating a sinusoidal carrier by an analog modulating signal
• Amplitude and angle modulation (frequency or phase modulation, depending on which parameter of the carrier is proportional to the modulating signal’s magnitude)
• Will not be dealt with in detail
• Amplitude modulation is being used for multiplexing several signals onto a single transmission channel, because it is
• Produced by multiplication in the time domain...
• which results in spectrum shift in the frequency domain
2.44. 4 SHARING A COMMON RADIO CHANNEL: MULTIPLEXING 2.45. Multiplexing: FDM and TDM
2.46. TDM - time division multiplexing
2.47. Wavelength division multiplexing
• Mentioning for completeness; it is a technique used in fibre optic communications channels
• It is essentially an FDM technique but called WDM in optical communications
2.48. CDM - code division multiplexing
• Neither frequency nor time separation
• How can it be?
• How can then the sources be distinguished?
• And what is it good for?
• Let us answer these questions by the example of direct sequence CDM-et!
2.49. Principle of code division multiplexing
• Analogy: humans communicating in a room
• TDM: talk one after the other, not the same time
• CDM: talk the same time but speak different languagues
• Principle: assigning individual specific codes to the sources (chip code)
• Chip codes are transmitted, resulting in spectrum spreading, signal uses the whole frequency band.
• Detection based on orthogonality of the chip codes
2.50. Principle of CDM, example
2.51. CDMA: advantages and disadvantages
• +:
• Eavesdropping is difficult, looks like a noise
• Not sensitive to narrow-band interference and multipath fading
• Frequency reuse in cellular systems
• -:
• Larger bandwidth proportionally to the chip code length
• Exact synchronization is needed at chip boundaries
2.52. 5 SHARING A COMMON RADIO CHANNEL: MULTIPLE ACCESS
2.53. Multiplexing multiple access
• Multiplexing:
• Common channel
• Many sources
• All at the same place, at the input of the channel
• Multiple access:
• Common channel
• Many sources
• Sources are spread over a certain territory which can be large
• In network protocol architectures the name is MAC (Medium Access Control)
2.54. Ways to divide a common channel ("fixed" methods)
• Multiple access companions of multiplexing techniques:
• FDMA TDMA CDMA
• FDMA
• Orthogonal, but difficult to implement
• Efficiency lower due to guard bands between adjacent channels inorder to ensure separability
• Applications for real-time traffic
• TDMA
• Orthogonal, good for flexible division, easy to create sub-channels of different size
• CDMA
• ...
• Interesting comment: what is SDMA (Space ...)?
• Separation of users in space
• Using directed antenna beams (smart antennas: e.g. MIMO - multiple input multiple output)
2.55. Example of a common radio channel: using a satellite repeater
2.56. Random access (random = free)
• Simple (pure) Aloha: entirely free access
2.57. The simple Aloha protocol
• Rules:
• Each terminal transmits when it has message to transmit
• It doesn't check whether the channel is idle
• Collisions are unavoidable, if a collision occurs no participant's transmission is successful
• They try again
• After a random delay!
• Simple and works: no coordination is needed, terminals don't have to know how many they are etc.
• Detecting a collision: automatic acknowledgements (sending on uplink-receiving - hearing back their own transmission on downlink)
2.58. "Slotted" Aloha
• Similar but time axis is "slotted", terminals can only start transmission at the beginning of a slot
• Consequently, either full overlap of packets or no overlap
• Probability of collisions smaller, utilization higher Performance of Aloha protocols
• Utilization: relatively low ( ) because channel cannot be heavily loaded as in this case it tends to become unstable (saturated)
• Delay: not bounded, but acceptable when traffic is not high
• Fairness: yes
2.59. Reservation Aloha
• By reservation, the channel throughput and delay can be improved
• Users send reservation messages using a (small) part of the channel bandwidth
• All users listen to the channel and hear about the reservation requests of others
• This way a reserved channel can be granted to users who successfully bidded for the channel
2.60. Applications of the Aloha protocol
• In a wireless environment, in cases where channel state cannot be sensed before transmitting
• No "carrier sensing", see later
• For bursty traffic, it is advantageous
• fixed allocation schemes are not efficient, cause delays (see later)
• but the traffic should be below 10%
• If the traffic grows beyond that, throughput falls quickly
• Application areas (mainly slotted Aloha):
• Satellite systems (tactical)
• RFID
• Together with reservation: GSM-GPRS
2.61. Carrier Sensing Multiple Access
• Using additional information from the channel: if it is idle or busy (commonly called carrier sensing)
• If the channel is idle:
• transmit
• If the channel is busy:
• Try later (non-persistent)
• Wait for the channel becoming idle (persistent):
• When idle, transmit immediately (1-persistent)- If collision: wait until a randomly chosen delay expires
• When idle, transmit with probability p (p-persistent)
2.62. Performance of carrier sensing multiple access
• A bit more complicated but still relatively simple implementation (only channel status - idle/busy - needs to be sensed)
• Significantly higher throughput can be achieved, in theory, it can be close to 100%
• Sensitive to the propagation delay, signal has to reach a station so that it can sense the channel busy.
Otherwise the information about the channel status can be outdated
• Can be unstable
• Fairness is granted
2.63. Centralized multiple access methods
• Polling: right to transmit is granted by a controller which polls the stations
• Probing: controller polls a group of stations
• If collision occurs (more than one station in the group want to transmit) it needs to be resolved
• Reservation: controller grants transmission right to a station for a specified time.
• Requests for the channel can be collected:
• Using a separate channel or part of a common channel for requests
• By competition
2.64. Roll-call polling
• Controller polls all stations one after the other
• If a station has message to transmit it sends
• Others are not allowed to transmit thus communication is contention-less
• Part of the time (of the available channnel throughput) is used for organizing the communication
• Throughput is the ratio of the to parts
• Access delay: bounded
• Stable and fair method
2.65. Probing
• Group polling:
• When collision, group is divided into subgroups
• Better channel utilization
• Lower acess delay
• Stability and
• Fairness granted
2.66. Reservation
• For large round-trip time, polling is not efficient
• Better to divide the channel into:
• Reservation part
• Transmission part
• The reservation part (constituting a small fraction of the total channel capacity):
• Dedicated to requests, based on
• Fixed allocation (e.g. TDMA)
• Contention (e.g. Aloha)
• Controller receives successful bids and grants access
2.67. Reservation: dividing the channel
2.68. 6 NETWORKING ASPECTS IN WIRELESS COMMUNICATIONS
2.69. Network topologies
• Point-to-point
• Point-to-multipoint (centralized)
• De-centralized (peer-to-peer)
• Broadcast
• Terrestrial
• Using a satellite repeater
• Self organizing topologies
• The cellular principle
2.70. Centralized topologies
• Communication between the nodes goes through a central station (hub or base station)
• The central station controls the nodes and the transmission from/to each node
• The central station manages the access by nodes to the network resources, allocates bandwidth
• Examples:
• Cellular networks
• WLAN, WMAN (in most cases)
• VSAT networks
2.71. Centralized topologies: advantages and disadvantages
• Advantages
• Nodes use less power to reach their peers compared with fully connected peer-to-peer since the communication goes through the hub
• Complex hub but simple nodes
• Hub can be placed on an optimal location
• Hub can provide connection to the backbone
• Disadvantages
• Single point of failure
• Delay in node-to-node communication due to two hops
• Cannot cover large areas
2.72. Decentralized topologies
• Also called peer-to-peer topology
• Fully connected network
• Any pair of nodes "see" each other (in radio comm. sense)
• Nodes communicate with each other directly
• Multi-hop networks (also called mesh topologies)
• Nodes cannot reach each other
• Intermediate nodes forward messages to the destinations
2.73. Fully connected network: advantages and disadvantages
• Advantages
• There is no single point of failure
• No store-and-forward delay
• No routing is needed, reduced complexity in nodes
• Disadvantages
• In large networks performance degradation
• Nodes need to increase transmit power to reach remote destinations
• Interferences
2.74. Multi-hop peer-to-peer network: advantages and disadvantages
• Advantages
• Nodes can operate at low transmitting power as they need to reach only the neighbors
• No infrastructure is needed, therefore
• Wide use in military, disaster recovery and similar areas
• Fault-tolerant, nodes can leave the network (because of failure or other reasons) of join, a kind of organic property
• Routing algorithms restore communication paths
• Total throughput of the network is high
• Use in ad hoc and sensor networks
• Disadvantages
• Complex routing algorithms are needed
• Performance degradation when traffic travels over multiple hops (nodes are mostly busy with forwarding)
• Therefore, in large networks a kind of infrastructure (backbone) is needed
2.75. Broadcast networks
• A special case of centralized topology
• Central station sends messages to all nodes
• Classic computer networks example: ALOHANET developed at the Univ. of Hawaii by Prof. Abramson
2.76. Literature
• Andreas F. Molisch: Wireless Communications, Wiley, 2011
• Theodore S. Rappaport: Wireless Communications. Theory and Practice. Edition. Prentice Hall, 2002
• ECE 245/445: Wireless Communications and Networking, Lecture Notes, Rochester University.
3. 3 WIRELESS LOCAL AND METROPOLITAN AREA NETWORKS
3.1. Contents
• Introduction
• Wireless LANs - Wi-Fi - IEEE 802.11
• 802.11 MAC layer
• Wi-Fi Mesh
• WiMAX - IEEE 802.16
• Application areas
• MAC and QoS
• Wi-Fi - WiMAX comparison
3.2. BWA- BROADBAND WIRELESS ACCESS: WLAN, WMAN
3.3. Family of wireless network technologies according to coverage area
3.4. WLANs and WMANs: coverage and data rates
3.5. Our objectives
• BWA is a big family of technologies characterized by:
• A number of different physical layer (radio) technologies
• Many medium access (MAC) protocols
• Numerous standards developed by several stadardization organizations
• Organizations supporting the introduction and penetration of BWA technologies.
• Objectives of our survey lecture?
• Overview of most important LAN-MAN standardized technologies,
• Concentrate on architectural aspects, and
• on the main characteristics of these technologies, and
• on the most important application areas to see how and to what extend the individual technologies meet the requirements of the given application
3.6. WIRELESS LANS - IEEE 802.11
WLAN - Wireless Local Area Network Wi-Fi - Wireless Fidelity
3.7. Wireless LANs?
• Main characteristics:
• Coverage of a few hundred meters
• Data rates from 1-2 Mbps to 54 Mbps, high speed WLANs: hundreds of Mbps
• Operation in the ISM (industrial-scientific-medical) unlicensed frequency band
• Typical applications, originally:
• Segments of LANs within building, in particular: hospitals, shopping centers, hotels, university campuses, protected buildings
• Connections between nearby buildings, e.g. across a street
• Temporary network installations for internet access in exhibition and conference areas
• Today:
• SOHO - small office - home office
• Public internet access points (hotspots)
3.8. WLAN devices
AccessPoint (AP)
3.9. 802.11 standards
• A family of sub-standards
• 802.11 - 1-2 Mbps, 2.4 GHz, FHSS
• 802.11a - 54 Mbps, 5 GHz, OFDM
• 802.11b - 11 Mbps, 2.4 GHz, DSSS, 11-13 channels
• 802.11g - 54 Mbps, 2.4 GHz, OFDM / DSSS, 13 channels
• 802.11n - up to 600 Mbps, 2.4 GHz, OFDM MIMO
• Additional sub-standards specifying important additional functionalities
• 802.11e - QoS support
• 802.11h - automatic power control (ATPC)and dynamic frequency selection (DFS)
• 802.11i - data security, encryption (e.g.: AES encryption)
• 802.11j - 802.11a - HiperLAN2 co-existence
• 802.11s - mesh mode operation
3.10. Channels (2.4 GHz band)
• E.g.: in the 2.4000-2.4835 GHz band, thirteen 22 MHz channels, separated by 5 MHz
• Spectral mask for every channel (because of overlappig)
• 30 dB attenuation at +/-11 MHz from the channel central frequency
• As an example, channels 1, 6 and 11 can be used without overlapping
• Interferences with home applicances and other communication devices: microwave oven, cordless phone, Bluetooth
• In the 5 GHz band: 23 non-overlapping channels
3.11. Physical layer technologies for wireless communications
3.12. 802.11 sub-standards corresponding to different physical
layer technologies
FHSS: frequency hopping spread spectrum DSSS: direct sequence spread spectrum
OFDM: orthogonal frequency division multiplexing
3.13. DSSS: detection, noise protection
• A bit is mapped to a -bit "chip", pseudo-random bit sequence of length
• Detection: correlation receiver, uses the pseudo-random bit sequence of the transmitter, synchronized
• Correlation detector yields maximum within the given chip time and low values at other places
• No correlation with noises and interferences
• Low correlation with interfering signals caused by multipath propagation
• Selection of the chip frequency ("processing gain"):
• Long code: good interference supression
• Short code: consumes less bandwidth
• IEEE 802.11 WLAN: 11 bit spreading
• FCC prescription: min. 10 in the ISM band
• This value is not too high: moderate interference supression, but acceptable bandwidth occupation
3.14. Frequency Hopping Spread Spectrum (FHSS)
• Uses multiple frequencies
• Example:
• 10 MHz sub-bands in the 50 MHz band
• First bit (or group of bits) is transmitted on 2.44 GHz, second bit on 2.41 GHz, third bit on 2.30 GHz
