Relay-Based Deployment Concepts for Wireless and Mobile Broadband Radio from IEEE Communication Magazine Sep. 2004

Relay-Based Deployment Concepts for Wireless and Mobile Broadband Radiofrom IEEE Communication Magazine Sep. 2004 Presented by Hermes YH Liu OPLAB, Dep. of Information Management, NTU

Authors • Ralf Pabst, Bernhard H. Walke, and Daniel C. Schultz, RWTH Aachen University • Patrick Herhold, Gerhard P. Fettweis Technical University of Dresden • Halim Yanikomeroglu, David D. Falconer Carleton University • Sayandev Mukherjee and Harish Viswanathan, Lucent Technologies • Matthias Lott and Wolfgang Zirwas, SIEMENS ICM • Mischa Dohler and Hamid Aghvami, Kings College OPLAB, Dep. of Information Management, NTU

Agenda • Introduction • The State of the Art • Multihop Operation • Cooperative Relaying and Virtual Antenna Arrays • Routing and Radio resource Management • WMS: A Prototypical Cellular Relay Network • Conclusions OPLAB, Dep. of Information Management, NTU

Introduction • Multihop-augmented infrastructure-based networks: 1. seed concept in 3GPP(3rd generation Partnership Project) 2. mesh networks in IEEE 802.16 3. coverage extension of HiperLAN/2 through relays or user-cooperative diversity mesh networks • Benefits via relays: 1. radio range extension (mobile and wireless broadband cellular network) 2. combat shadowing at high radio frequencies 3. reduce infrastructure deployment costs 4. enhance capacity in cellular networks OPLAB, Dep. of Information Management, NTU

Introduction • 4G cellular systems do not feasible with the current cellular architecture due to: 1. the transmission rates of 4G are two orders of magnitude higher than 3G, this creates power concerns: –for a given transmit power level, the symbol/bit energy ( , energy per symbol/ bit) decreases linearly with the increasing transmission rate 2. The spectrum for 4G will be located 2GHz above 3G, the radio propagation is significantly more vulnerable to non-line-of-sight (non- LOS), which is typical mode of today’s urban cellular system OPLAB, Dep. of Information Management, NTU

Introduction • Drawbacks of increase the density of base stations (BS): 1. deployment cost 2. transmission cost (data/bit vs. voice/bit) OPLAB, Dep. of Information Management, NTU

Introduction • Virtue of multihop wireless network: 1. transmit power is significantly reduced – conventional cellular networks have cells of diameter 2-5 km, while relay has 200- 500 m in diameter – relay does not need to be as high as BS, reducing tower leasing and maintenance costs 2. relays are wireless 3. solving coverage problem for high data rates in larger cells 4. capacity gains can be achieved with reuse efficiency or spatial diversity OPLAB, Dep. of Information Management, NTU

Introduction • Virtue of multihop wireless network: 5. the relay-to-user links could use different (unlicensed) spectrum (e.g., IEEE 802.11x) than the BS-to-user links (licensed spectrum) 6. Do not need complicated distributed routing algorithms as ad hoc networks — ad hoc: function without any infrastructure — relay: very-high-data-rate coverage and throughput OPLAB, Dep. of Information Management, NTU

The State of the Art • Bidirectional amplifiers have been used in 2G and 3G systems —analog repeaters, increase noise and suffer instability • ETSI/DECT standard in 1998 was the first specifying fixed relays (called wireless BSs) for cordless systems using TDM channels for voice and data communications • TDMA, F/TDMA, CDMA, FDD (uplink and downlink)…., and can easily be extended to packet-based systems • ETSI- broadband radio access network (BRAN), high-performance LAN (HiperLAN/1,2), IEEE 802.11x have elements to operate ad hoc networks OPLAB, Dep. of Information Management, NTU

The State of the Art • Relaying systems: — decode-and forward: digital repeaters, bridges, or routers. Regenerate the signal by fully decoding and reencoding the signals prior to retransmission — amplify-and forward: analog repeater, increase the noise level OPLAB, Dep. of Information Management, NTU

Multihop Operation The intersection can be covered well by the AP. Nearby streets can only be served if line-of-sight (LOS) connectivity is available between a mobile terminal and its serving station, due to the difficult radio propagation condition, ex. In the 5-6 GHz frequency band Figure 1.a Manhattan scenario with one AP (serving the white area) and four RSs covering the shadowed areas around the corners shown in beige. OPLAB, Dep. of Information Management, NTU

Multihop Operation RS have to route the traffic to AP for two ways: 1. Via intermediate RS using a low-rate but robust combination modulation and coding (PHY mode) 2. Via RSs and using a faster PHY mode and thus higher link capacity Figure 2. a schematic of Manhattan scenario OPLAB, Dep. of Information Management, NTU

Multihop Operation The basic element of Fig. 1 can be repeated to cover a wide area Figure 3. wide-area coverage using the basic element OPLAB, Dep. of Information Management, NTU

Multihop Operation a) AP and RSs operating at the same carrier frequency while accessing the physical medium in time multiplex b) AP and RSs operating at different carrier frequencies c) A fixed RS operate to bridge the distance between AP and the second RS where direct communication between the AP and the second RS is not possible due to lack of LOS Figure 4. Examples of relay concepts OPLAB, Dep. of Information Management, NTU

Multihop Operation Figure 5. Analytical estimation of the extension of the radio range of an AP by relays with receive antenna gain OPLAB, Dep. of Information Management, NTU

Multihop Operation • Relaying function in OSI reference model: Physical: repeater link: bridge network: router OPLAB, Dep. of Information Management, NTU

Multihop Operation Figure 6. Left: a fixed wireless router at an intersection to extend the radio range of an AP around the corner into a shadowed area to serve a remote mobile terminal. Right: maximum end-to-end throughput vs. distance for forwarding under LOS conditions with directed receive antennas having a gain of 11 dB OPLAB, Dep. of Information Management, NTU

Multihop Operation • Benefits of relaying summary: — throughput — coverage — radio resource reuse (ex. frequency reuse) — cost advantage OPLAB, Dep. of Information Management, NTU

Cooperative Relaying and Virtual Antenna Arrays • Conventional relay: store-and-forward in a relay chain. A receiver solely copy the data sent by its respective transmitter, while discards emissions from other transmitters • Cooperative relay: 1. broadcast nature 2. achieve diversity through independent channels A signal, once transmitted, can be received (and usually forward) by multiple terminals OPLAB, Dep. of Information Management, NTU

Cooperative Relaying and Virtual Antenna Arrays Virtual antenna arrays: each relay becomes part of a larger distributed array Challenge: synchronization, availability of channel state information, and appropriate cluster formation Figure 8. The concept of cooperative relay (a) OPLAB, Dep. of Information Management, NTU

Cooperative Relaying and Virtual Antenna Arrays • Benefits of cooperative relay: 1. path loss saving 2. power gain — each of the relays add additional transmit power combined in the destination terminal 3. macrodiversity gain allows combating shadowing The integration of multiple-input-multiple-output (MIMO) and so-called dirty paper coding techniques may lead to advanced multihop networks with high spectral efficiency OPLAB, Dep. of Information Management, NTU

Cooperative Relaying and Virtual Antenna Arrays • Type of cooperative protocols: 1. static: the relay nodes constantly retransmit data of their received signals 2. adaptive: allowing feedback and/or signaling between forwarding nodes, the relays resend signals only when they believe it to be helpful for the destination node. The adaptation may be done independently or jointly for all relays if information is exchanged between the relays OPLAB, Dep. of Information Management, NTU

Cooperative Relaying and Virtual Antenna Arrays Virtual antenna array: Group together closely spaced relays to form a stage. The source node transmits to the relays in the first stage, which then use space-time coding in a distributed manner to retransmit the signal to the next stage Figure 9. The concept of cooperative relay (b) Figure 10. Space-time coding OPLAB, Dep. of Information Management, NTU

Routing and Radio resource Management • Routing algorithms for mobile ad hoc network (MANET) have high routing overhead and low efficiency in network throughput • It is proposed that routing in the multihop network be supported by an area-wide cellular overlay network, where route requests are sent to the BS of the overlaying cellular networks which called Cellular Based Multihop (CBM) routing • Determines the route and responds with a packet comprising a series of mobile nodes willing to relay the data traffic between the source and destinations • Both macro network to communicate with all nodes and throughput efficiency of multihop transmission in the microrange layer OPLAB, Dep. of Information Management, NTU

Routing and Radio resource Management Figure 11. Hierarchical system architecture for a Service Specialized System (SSS) OPLAB, Dep. of Information Management, NTU

Routing and Radio resource Management Figure 12. comparison delivery rate and delay of CBM (Cellular Based Multihop) and DSR (Dynamic Source Routing) CBM delivers more packets and has minimum delay– leads to less packet drops due to wrong route information OPLAB, Dep. of Information Management, NTU

Routing and Radio resource Management • Radio resource management: 1. performance gains due to no. relays increase when terminals increase 2. the maximum relay transmit power is important only in large cells 3. performance gains are quite sensitive to the relay selection criterion — wrong relay is worse than no relay 4. once a good relay is selected, performance gains becomes fairly insensitive to the relay channel selection criterion 5. selection criteria involve the mutual interference between relay channels OPLAB, Dep. of Information Management, NTU

Figure 13. Wireless media system: integration with mobile radio OPLAB, Dep. of Information Management, NTU

WMS: A Prototypical Cellular Relay Network • Wireless Media System (WMS): 1. intended to have very high multiplexing data rate between 100-1000 Mb/s, the spectrum bands (ex. Beyond 3GHz, or even 5GHz) will allow very small equipment size for picocellular BSs/APs and RSs, including the antennas 2. WMS is integrated into a 3G system sharing — An IPv6 based fixed core network — Functions of the cellular system like subscriber identity module (SIM), Authentication, authorization, and accounting (AAA), and localization 3. both APs and RSs appear like a BS to a mobile terminal 4. cost efficient and flexible infrastructure OPLAB, Dep. of Information Management, NTU

Conclusions • Cooperative use of relays forming virtual antenna arrays to exploit the spatial diversity leading to increases in available capacity • WMS, a concept for a mobile broadband system based on fixed relay stations • Multihop communications can provide a substantial increase in network capacity when suffering from heavy path loss • The very high capacity can be traded for radio range which would otherwise be limited due to high attenuation at high radio frequencies OPLAB, Dep. of Information Management, NTU

Conclusions • Future works: 1. virtual arrays 2. multiple access and multiplexing schemes 3. combination of medium access and radio resource management protocols for multihop networks 4. relay system in IEEE 802.16j Relay OPLAB, Dep. of Information Management, NTU

The End Thanks for Listening!! OPLAB, Dep. of Information Management, NTU

3G vs. 4G OPLAB, Dep. of Information Management, NTU

Definitions • Reuse efficiency: a radio channel which is occupied in one microzone can be used in adjacent microzones • Spatial diversity: one of the antenna diversity techniques, uses multiple antennas, antennas arrays to transmit/receive signals OPLAB, Dep. of Information Management, NTU

Definitions • Gain: An antenna characteristic that increases the power density in a given direction by concentration of radiated energy • Gain is given in reference to a standard antenna. An antenna gain of 2 (3 dB) compared to an isotropic antenna would be written as 3 dBi. An antenna gain of 1 (0 dB) compared to a dipole antenna would be written as 0 dBd • Use the following conversion factor to convert between dBd and dBi: 0 dBd = 2.15 dBi OPLAB, Dep. of Information Management, NTU

Definitions • MIMO: MIMO algorithms in a radio chipset send information out over two or more antennas. The radio signals reflect off objects, creating multiple paths that in conventional radios cause interference and fading. But MIMO uses these paths to carry more information, which is recombined on the receiving side by the MIMO algorithms (http://www.networkworld.com) • MIMO can also be used in conjunction with OFDM, and is part of the IEEE 802.16 standard and will also be part of the IEEE 802.11n High-Throughput standard, which is expected to be finalized in mid 2007. Standardization of MIMO to be used in 3G standards such as HSDPA is currently under way. • Spectral efficiency: bit/sec/Hz OPLAB, Dep. of Information Management, NTU

Definitions • Dirty paper coding: dirty-paper coding means techniques that allow a transmitter to send information so that each use sees no interference from other users From IEEE SIGNAL PROCESSING MAGAZINE OPLAB, Dep. of Information Management, NTU

Relay-Based Deployment Concepts for Wireless and Mobile Broadband Radio from IEEE Communication Magazine Sep. 2004