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... user (SU) and multiple users (MU)sMIMO and explain various linear and non-linear precoding and detection techniques usedsin MIMO.s2.4.1 Single-User MIMO (SU-MIMO)sSU-MIMO as the name suggests [3][41]=-=[42]-=-, involves a point to point transmission where assingle transmitter equipped with ...

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...ngle user (SU) and multiple users (MU)sMIMO and explain various linear and non-linear precoding and detection techniques usedsin MIMO.s2.4.1 Single-User MIMO (SU-MIMO)sSU-MIMO as the name suggests [3]=-=[41]-=-[42], involves a point to point transmission where assingle transmitter equipped with ...

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....sAlso the BS needs to know the interuser channel information for optimal decoding.sHowever, the first practical cooperation schemes based on time division among users wassproposed by Laneman in [100]=-=[101]-=-where nodes transmit their data using separate timesslots each consisting of B channel uses in the non-cooperative case. When they cooperate,seach user divides its time slot into two equal periods.sIn...

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...fficiency. Insthe literature many research work has been conducted to find optimum trainingssequences [6]. A well-known example of training based estimation technique is leastssquares (LS) estimation =-=[7]-=-.s• Blind channel estimation: In these techniques the estimator relies on the statisticalsknowledge of the fading channel or data. Blind estimation requires complex processessthat often have slow conv...

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...catterers such as building, cars, trees, ground terrain, orsthe atmosphere (atmospheric ducting and ionospheric reflection) in outdoor scenarios, orswalls, furniture, and people in indoor scenario [4]=-=[3]-=- [3].sThis causes the radio signal to reflect of, refract through, or diffuse around these scatteringsobstacles, which not only dissipate signal power causing path or propagation loss, but alsosthese ...

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...ising spatial diversity gain or increase thessystem capacity through spatial multiplexing. The first is usually referred to in literature assD-BLAST while the second is called V-BLAST architecture [3]=-=[55]-=-[56].sThe essential difference between the two architectures lies in how data streams are encoded.sIn D-BLAST, redundancy between the data streams is introduced through the use ofsspecialized space-ti...

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... saving, and extended cells152scoverage. The origin of cooperative communication can be traced to the pioneering work bysVan der Meulen [97] who introduced the relay channel and by Cover and El Gamal =-=[98]-=-swho proposed a number of relaying schemes and analysed the capacity of the degradedsrelay channel. Despite the importance of their work, cooperative communication is differentsthan relay networks in ...

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...g spatial diversity gain or increase thessystem capacity through spatial multiplexing. The first is usually referred to in literature assD-BLAST while the second is called V-BLAST architecture [3][55]=-=[56]-=-.sThe essential difference between the two architectures lies in how data streams are encoded.sIn D-BLAST, redundancy between the data streams is introduced through the use ofsspecialized space-time b...

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...QAM modulation with rate Msbits/channel usestransmitting over a bandwidth W to maintain a specified bit error rate BER under channelsinversion adaptation policy can be obtained by modifying Eq. 26 in =-=[81]-=- and is given bys...

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...degradation in the sum rate capacity and bitserror rate (BER) performance [64]. Thirdly, the amount of overhead increase with thesnumber of users both in terms of pilots needed for channel estimation =-=[68]-=-[69]sand for usersscheduling and precoding [65].sIn this chapter, we propose a bandwidth efficient NOMAS called CMMA that utilises wellsknown technologies like SPC, adaptive modulation, precoding, and...

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...ense of doublingsthesbandwidthscompared withsdirect transmission for a givensrate.sTo avoid the use of repetition coding and maintain the same rate as in direct transmission,sHunter proposed in [102] =-=[103]-=- [104] [105] coded cooperation where cooperation issintegrated with channel coding. In coded cooperation, each user will encode K informationsinto B coded bits per block, so that R = K/B. Then the N b...

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...res the extensively complexs53smultidimensional Viterbi algorithm. Space-time block codes (STBC) on the other handsattains only a diversity order equal to ...

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....5 Orthogonal Frequency Division Multiple Access (OFDMA)sOrthogonal frequency division multiplexing (OFDM) is a narrowband orthogonal multicarrier MAS used for LTE and 4G networks [1] [26][26][27][28]=-=[29]-=-. In OFDM, thesinformation to be transmitted is mapped onto several parallel overlapping sub-carrierss43swhich are chosen so that they are orthogonal to each other by separating the carriers bys...

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... designated time slots .sFrequency C od e U se r 1 U se r 2 U se r 3 U se r K Figure 2- 3 Time, frequency, and code illustration of TDMAs39s2.3.3 Coding Division Multiple Access (CDMA)sCDMA [3][4][19]=-=[20]-=-[21][31] allows multiple users to access the network simultaneouslysand over the same bandwidth by multiplying the data of each user by a unique spreadingscode with a rate much higher than that of the...

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...s feedback and channel measurements [86].sThe capacity of a single input single output system using multiuser diversity and adaptivesand adaptive transmission with variable rate and power is given in =-=[83]-=- by :sℂ...

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...lingsthesbandwidthscompared withsdirect transmission for a givensrate.sTo avoid the use of repetition coding and maintain the same rate as in direct transmission,sHunter proposed in [102] [103] [104] =-=[105]-=- coded cooperation where cooperation issintegrated with channel coding. In coded cooperation, each user will encode K informationsinto B coded bits per block, so that R = K/B. Then the N bits codeword...

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...le usersL=2, 16 QAM single usersL=3,sMax(dmin) precodersL=3,sMMSE Linear precodersL=1,sCMMAsL=2,sCMMAsL=3,sCMMA 93sscheme over which 2 independent data streams are sent employing MMSE linear precoders=-=[76]-=- and max mindsprecoder [77] with ML detection and assuming perfect CSI available atsboth transmitter and receiver side. Even with the reduced complexity and feedback overheadscompared to [24-25], CMMA...

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...tion systemsOptimal performance can be achieved by switching between the two schemes to achieveshigh spectral efficiency without comprising BER performance also referred to adaptivesMIMO switch (AMS) =-=[48]-=-. A number of schemes have been proposed in literature tosoptimize this switching like [50]which is based on SNR information and time/frequencysselectivity indicators and [51] which exploits the spati...

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...ically send data to the user closest to the beam. Dumb antenna cansapproach the performance of true beamforming when the number of users is large, but withsmuch less feedback and channel measurements =-=[86]-=-.sThe capacity of a single input single output system using multiuser diversity and adaptivesand adaptive transmission with variable rate and power is given in [83] by :sℂ...

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...r opportunistic feedback approach forsCMMA-OS.s5.2.2.2.1 Related worksExcessive feedback, especially when the number of users is large, can outweigh anysbenefits derived from opportunistic scheduling =-=[93]-=-, therefore the issue of reducing thesamount of required feedback has been an active area of research. In [93], a simple thresholdsbased scheme restricts feedback only to users whose channel gain is a...

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...f doublingsthesbandwidthscompared withsdirect transmission for a givensrate.sTo avoid the use of repetition coding and maintain the same rate as in direct transmission,sHunter proposed in [102] [103] =-=[104]-=- [105] coded cooperation where cooperation issintegrated with channel coding. In coded cooperation, each user will encode K informationsinto B coded bits per block, so that R = K/B. Then the N bits co...

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...te per sub-carrier increase, time and frequency synchronization becomessvery difficult leading to frequency offset, and intolerable ICI.sHence combining CDMAswith OFDM known as Multi-carrier CDMA [26]=-=[30]-=- is beneficial for both systems as it cans46slower the symbol rate at each sub-carrier so that a longer symbol time is easier tossynchronise and maintain frequency orthogonally.sMulti-carrier CDMA ret...

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...nnels.sAlso the BS needs to know the interuser channel information for optimal decoding.sHowever, the first practical cooperation schemes based on time division among users wassproposed by Laneman in =-=[100]-=-[101]where nodes transmit their data using separate timesslots each consisting of B channel uses in the non-cooperative case. When they cooperate,seach user divides its time slot into two equal period...

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...ingle-antenna mobile terminals which reduces thescomplexity, size, and cost of mobile terminals.sUnfortunately realizing the full benefits of MU-MIMO is constrained by a number ofsfactors [64][65][66]=-=[67]-=-s• Unlike SU-MIMO, MU-MIMO requires the availability of CSIT for the downlink; thissplaces a significant burden on users which have to feedback their CSI to the BS, thes56soverhead per user increases ...

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...ZF has the lowest complexity of allsschemes however it offers no diversity gain while the optimum ML detection can retain asdiversity order equal to ...

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...ieveshigh spectral efficiency without comprising BER performance also referred to adaptivesMIMO switch (AMS) [48]. A number of schemes have been proposed in literature tosoptimize this switching like =-=[50]-=-which is based on SNR information and time/frequencysselectivity indicators and [51] which exploits the spatial selectivity of the channel.s54s2.4.2 Multiuser MIMO (MU-MIMO)sMU-MIMO allows multiple us...

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...val, and received power between thatsmobile user and a number of nearby BSs. Alternatively, a mobile user equipped with a GPSsreceiver can locally calculate its location and then forward it to the BS =-=[80]-=-.sOnce theslocation of that user is obtained, field measurement stored at the BS can be used to obtainsthe average channel gain associated with that location.s3.8.2 Minimum distance selection criteria...

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... practical systems where feedback is usually done in asTDMA manner thus the feedback period increases linearly with the number of users.sTo address this issue, opportunistic splitting was proposed in =-=[94]-=- where each datastransmission is preceded by a number of mini slots, which the BS uses to obtain the currentsCSI of users in a distributed manner. Once the user with strongest channel is identified, d...

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... coded cooperation, Hunter employed Rate154sCompatible Punctured Convolutional (RCPC) codes in [102] and space-time and turboscoding in [105] which are more suitable in fast fading scenarios.sChen in =-=[106]-=- proposed a network coding approach to cooperation to enable more than twosusers to cooperate thus achieving a diversity gain in the order of the number of users whilesmaintaining a fair distribution ...

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... are in the same region), thenstheir feedback messages will not collide, since each user uses a unique modulation set. Thatsis contrary to the commonly used approach of Opportunistic Feedback (OF) in =-=[95]-=- [96],swhere the SP is divided into a number of time slots and the pdf of the channel gain issquantized into one of these slots. The BS will then simply arrange users in the order of theirschannel gai...

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...tion of SDMAs2.3.5 Orthogonal Frequency Division Multiple Access (OFDMA)sOrthogonal frequency division multiplexing (OFDM) is a narrowband orthogonal multicarrier MAS used for LTE and 4G networks [1] =-=[26]-=-[26][27][28][29]. In OFDM, thesinformation to be transmitted is mapped onto several parallel overlapping sub-carrierss43swhich are chosen so that they are orthogonal to each other by separating the ca...

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...SDMAs2.3.5 Orthogonal Frequency Division Multiple Access (OFDMA)sOrthogonal frequency division multiplexing (OFDM) is a narrowband orthogonal multicarrier MAS used for LTE and 4G networks [1] [26][26]=-=[27]-=-[28][29]. In OFDM, thesinformation to be transmitted is mapped onto several parallel overlapping sub-carrierss43swhich are chosen so that they are orthogonal to each other by separating the carriers b...

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... BS and its partners. However, during thessecond time slot it will combine the data received from its partners during previous timesslots using linear network coding and transmits the result.sXiao in =-=[107]-=- proposed another network coding approach to cooperative diversity featuringsthe algebraic superposition of convolutional channel codes over a finite field.sEach userswill pseudo-randomly interleave p...

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...6m and Long Term Evolutionsadvanced (LTE)-Advanced and the ITU’s IMT-Advanced, all envisage the concurrentsdeployment of a number of compatible technologies in the physical and multiple accessslayers =-=[1]-=-.sOne of these key technologies is multi-carrier multiple access schemes (MAS) which aresbased on orthogonal frequency division multiplexing such as OFDMA and multi-carriersCDMA. These schemes enable ...

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... low performance of blind methods are compensatedsby combining small training sequences and statistical knowledge of the requiredsparameters in order to improve the performance of the estimator [8][9]=-=[10]-=-.s• Superimposing –based estimation: There is a wide range of channel estimationsmethods which embed the training sequence to the data and namely are known as pilotshiding[11], implicit[12], and super...

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...le user (SU) QAM using the same order constellation as that of MUQAM. However, various schemes proposed to reduce the complexity of ML in point to pointscommunication or for MIMO like sphere decoding =-=[71]-=- and multistage ML detection [72]scan greatly reduce the complexity of ML for CMMA with a very modest reduction in BERsperformance. For example, for 6x6 MIMO system employing QPSK modulation, [72] can...

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...fsreceive-transmit antennas, MIMO attains a linear increase in system capacity in the order ofsminimum number of received /transmit antennas ...

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...he codewords immediately before and after a given codeword is used in processing thatscodeword. After B iterations, the decoder makes a decision and the window is advanced bysone codeword.sLarsson in =-=[108]-=- proposed a similar scheme to Xiao in which users simultaneously transmitstheir own data packet and the packet for which they act as relay by using superpositionscoding instead of network coding with ...

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...ellular networks). In the following sections, the mainscharacteristics of some important multiple access techniques are briefly reviewed.s2.3.1 Frequency Division Multiple Access (FDMA)sFDMA[3][4][17]=-=[18]-=- was the first MAS used for cellular networks due to its ease ofsimplementation in analogous continuous communications. FDMA divides the available cellsbandwidth W into N frequency channels thus it ca...

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...sers designated time slots .sFrequency C od e U se r 1 U se r 2 U se r 3 U se r K Figure 2- 3 Time, frequency, and code illustration of TDMAs39s2.3.3 Coding Division Multiple Access (CDMA)sCDMA [3][4]=-=[19]-=-[20][21][31] allows multiple users to access the network simultaneouslysand over the same bandwidth by multiplying the data of each user by a unique spreadingscode with a rate much higher than that of...

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...(Pr(...

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...ignated time slots .sFrequency C od e U se r 1 U se r 2 U se r 3 U se r K Figure 2- 3 Time, frequency, and code illustration of TDMAs39s2.3.3 Coding Division Multiple Access (CDMA)sCDMA [3][4][19][20]=-=[21]-=-[31] allows multiple users to access the network simultaneouslysand over the same bandwidth by multiplying the data of each user by a unique spreadingscode with a rate much higher than that of the use...

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...This channelsis modelled as a complex Gaussian-distributed with zero-mean and unit variance. We willsgenerate N uncorrelated fading channels with Rayleigh distribution usingsimproved sum ofssinusoids =-=[78]-=- where ascomplex Gaussian noise is generated bysfinite sum of weightedssinusoids. The baseband representation of ...

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...osing –based estimation: There is a wide range of channel estimationsmethods which embed the training sequence to the data and namely are known as pilotshiding[11], implicit[12], and superimposed [13]=-=[14]-=- training techniques. Inssuperimposing the training sequence is arithmetically added to the information data. Insthis way, no bandwidth is lost for training sequence. To make use of the trainingsseque...

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...rimposing –based estimation: There is a wide range of channel estimationsmethods which embed the training sequence to the data and namely are known as pilotshiding[11], implicit[12], and superimposed =-=[13]-=-[14] training techniques. Inssuperimposing the training sequence is arithmetically added to the information data. Insthis way, no bandwidth is lost for training sequence. To make use of the trainingss...

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...set any costs enabling higher throughput, reliability, net power saving, and extended cells152scoverage. The origin of cooperative communication can be traced to the pioneering work bysVan der Meulen =-=[97]-=- who introduced the relay channel and by Cover and El Gamal [98]swho proposed a number of relaying schemes and analysed the capacity of the degradedsrelay channel. Despite the importance of their work...

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...ss cellular networks). In the following sections, the mainscharacteristics of some important multiple access techniques are briefly reviewed.s2.3.1 Frequency Division Multiple Access (FDMA)sFDMA[3][4]=-=[17]-=-[18] was the first MAS used for cellular networks due to its ease ofsimplementation in analogous continuous communications. FDMA divides the available cellsbandwidth W into N frequency channels thus i...

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...aptivesMIMO switch (AMS) [48]. A number of schemes have been proposed in literature tosoptimize this switching like [50]which is based on SNR information and time/frequencysselectivity indicators and =-=[51]-=- which exploits the spatial selectivity of the channel.s54s2.4.2 Multiuser MIMO (MU-MIMO)sMU-MIMO allows multiple users equipped with a single or multiple antennas toscommunicate with a BS equipped wi...

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... a single-antenna mobile terminals which reduces thescomplexity, size, and cost of mobile terminals.sUnfortunately realizing the full benefits of MU-MIMO is constrained by a number ofsfactors [64][65]=-=[66]-=-[67]s• Unlike SU-MIMO, MU-MIMO requires the availability of CSIT for the downlink; thissplaces a significant burden on users which have to feedback their CSI to the BS, thes56soverhead per user increa...

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...ng channels.sNOMAS can also be realized without any form of coding by exploiting the spatial or/andstemporal disparities in the received SNR of multiple users using superposition coding (SPC)s[57][61]=-=[62]-=-. SPC employs multistage detection technique referred to as successivesinterference cancellation (SIC) [62]. SPC with effective power control and scheduling hassbeen proven to increase the system capa...

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...s2.3.5 Orthogonal Frequency Division Multiple Access (OFDMA)sOrthogonal frequency division multiplexing (OFDM) is a narrowband orthogonal multicarrier MAS used for LTE and 4G networks [1] [26][26][27]=-=[28]-=-[29]. In OFDM, thesinformation to be transmitted is mapped onto several parallel overlapping sub-carrierss43swhich are chosen so that they are orthogonal to each other by separating the carriers bys...

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... single or multiple antennas toscommunicate with a BS equipped with a multiple antenna by exploiting the spatialsdimension between users who transmit simultaneously and over the same bandwidths[3][52]=-=[53]-=-. MU-MIMO shares many of the principles and technologies used in SU-MIMOsespecially in uplink communication. However since users can’t jointly decode their datasstreams in the downlink and are unaware...

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...he training sequences aresoften long and introduce large overhead resulting in reduced bandwidth efficiency. Insthe literature many research work has been conducted to find optimum trainingssequences =-=[6]-=-. A well-known example of training based estimation technique is leastssquares (LS) estimation [7].s• Blind channel estimation: In these techniques the estimator relies on the statisticalsknowledge of...

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...idely used in wirelesss38scellular networks (such as Global System for Mobile Communications (GSM) and GeneralsPacket Radio Service (GPRS))sas a complementary multiple access scheme to FDMAs[3][4][17]=-=[31]-=-as illustrated in Figure 2- 3 , TDMA allows each user to transmit using thesentire available bandwidth for a portion of the time. Each frequency channel is divided intosa number of periodically recurr...

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...f CSI are required (full,sstatistical, or partial)sand the overhead or cost associated with estimation. However mostschannel estimation scheme fall into four main categoriess• Pilot-based estimation: =-=[5]-=-pilots also known as training sequences are a block of datastransmitted which is known at the receiver and is used to determine the unknownsparameters. This category of estimation techniques provide a...

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...ator [8][9][10].s• Superimposing –based estimation: There is a wide range of channel estimationsmethods which embed the training sequence to the data and namely are known as pilotshiding[11], implicit=-=[12]-=-, and superimposed [13][14] training techniques. Inssuperimposing the training sequence is arithmetically added to the information data. Insthis way, no bandwidth is lost for training sequence. To mak...

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...and low performance of blind methods are compensatedsby combining small training sequences and statistical knowledge of the requiredsparameters in order to improve the performance of the estimator [8]=-=[9]-=-[10].s• Superimposing –based estimation: There is a wide range of channel estimationsmethods which embed the training sequence to the data and namely are known as pilotshiding[11], implicit[12], and s...

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...hether TDD or FDDsis used to separate between the uplink and downlink channels. Usually the feedback is sentsevery 0.67ms from the BS to users to adapt their power up or down in the range of 0.5-1 dBs=-=[22]-=-.sEqual power control between users minimise the co-channel interference at the BS howeversthat comes at the expense of low sum rate since the rate per user is limited to that with thesweakest channel...

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...sing a single-antenna mobile terminals which reduces thescomplexity, size, and cost of mobile terminals.sUnfortunately realizing the full benefits of MU-MIMO is constrained by a number ofsfactors [64]=-=[65]-=-[66][67]s• Unlike SU-MIMO, MU-MIMO requires the availability of CSIT for the downlink; thissplaces a significant burden on users which have to feedback their CSI to the BS, thes56soverhead per user in...

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...in the same region), thenstheir feedback messages will not collide, since each user uses a unique modulation set. Thatsis contrary to the commonly used approach of Opportunistic Feedback (OF) in [95] =-=[96]-=-,swhere the SP is divided into a number of time slots and the pdf of the channel gain issquantized into one of these slots. The BS will then simply arrange users in the order of theirschannel gains an...

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...ed using a single-antenna mobile terminals which reduces thescomplexity, size, and cost of mobile terminals.sUnfortunately realizing the full benefits of MU-MIMO is constrained by a number ofsfactors =-=[64]-=-[65][66][67]s• Unlike SU-MIMO, MU-MIMO requires the availability of CSIT for the downlink; thissplaces a significant burden on users which have to feedback their CSI to the BS, thes56soverhead per use...

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...ith the channel coherent time is small or/and the number of users areslarge. To overcome this coordination problem, a random access based feedback protocolscalled static splitting was proposed in [91]=-=[92]-=-, where only users transmit to the BS duringsthe feedback stage. Here, each data transmission is preceded by a fixed number of minisslots. In each mini slot, users with instantaneous channel gain abov...

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...ns and low performance of blind methods are compensatedsby combining small training sequences and statistical knowledge of the requiredsparameters in order to improve the performance of the estimator =-=[8]-=-[9][10].s• Superimposing –based estimation: There is a wide range of channel estimationsmethods which embed the training sequence to the data and namely are known as pilotshiding[11], implicit[12], an...

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...ransmit constantly regardless of relative channel correlation, thesprobability density function (PDF) of the received signal amplitude assuming Raleigh fadingsis simply that of a single usersgiven by =-=[82]-=- as Pr(λ) = ...

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...e of the estimator [8][9][10].s• Superimposing –based estimation: There is a wide range of channel estimationsmethods which embed the training sequence to the data and namely are known as pilotshiding=-=[11]-=-, implicit[12], and superimposed [13][14] training techniques. Inssuperimposing the training sequence is arithmetically added to the information data. Insthis way, no bandwidth is lost for training se...

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...frequency and codesdimensions of MC-CDMA and MC-DS-CDMA techniques.sFigure 2- 7 : Time, frequency and code dimensions of MC-CDMA and MC-DS-CDMA.s2.3.7 Collaborative Coding Multiple Access (CCMA)sCCMA =-=[32]-=-[33][34][35][36][37][39][40] is narrowband non-orthogonal MAS which allowssseveral users to transmit simultaneously over a common channel without any subdivision instime, frequency, or code. Hence unl...

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...uency and codesdimensions of MC-CDMA and MC-DS-CDMA techniques.sFigure 2- 7 : Time, frequency and code dimensions of MC-CDMA and MC-DS-CDMA.s2.3.7 Collaborative Coding Multiple Access (CCMA)sCCMA [32]=-=[33]-=-[34][35][36][37][39][40] is narrowband non-orthogonal MAS which allowssseveral users to transmit simultaneously over a common channel without any subdivision instime, frequency, or code. Hence unlike ...

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...fading channels.sNOMAS can also be realized without any form of coding by exploiting the spatial or/andstemporal disparities in the received SNR of multiple users using superposition coding (SPC)s[57]=-=[61]-=-[62]. SPC employs multistage detection technique referred to as successivesinterference cancellation (SIC) [62]. SPC with effective power control and scheduling hassbeen proven to increase the system ...

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...adation in the sum rate capacity and bitserror rate (BER) performance [64]. Thirdly, the amount of overhead increase with thesnumber of users both in terms of pilots needed for channel estimation [68]=-=[69]-=-sand for usersscheduling and precoding [65].sIn this chapter, we propose a bandwidth efficient NOMAS called CMMA that utilises wellsknown technologies like SPC, adaptive modulation, precoding, and joi...

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... adding any extra time slots compared with directscommunication.sReducing the effect of half duplex constraint can also be achieved with spatial multiplexing.sThis concept was introduced by Kannan in =-=[110]-=-[101] which proposed a Space DivisionsRelaying (SDR) that allows two users to exchange their data in first and second periods, andsin the third period, space division multiplexing rather than time div...

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...rder constellation as that of MUQAM. However, various schemes proposed to reduce the complexity of ML in point to pointscommunication or for MIMO like sphere decoding [71] and multistage ML detection =-=[72]-=-scan greatly reduce the complexity of ML for CMMA with a very modest reduction in BERsperformance. For example, for 6x6 MIMO system employing QPSK modulation, [72] cansachieve the BER performance clos...

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...void fading correlation.sAt the BS antenna separation in the order of 10 wavelengthss52s(1.5m at 2GHz) is required; whilesmore than half a wavelength at the mobile handsets(7.5cm at 2GHz) is required =-=[44]-=- [45].sn1 nNr h11 h1Nr hNt1 hNtNr 1 Nr H y1 yNr ^ b1 b̂NtbNt x1 xNt b1 DS P DS P Tx Rx 1 Nt Figure 2- 9 Illustration of a SU-MIMO systemsDepending on the average received SNR, SU-MIMO can be used eith...

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...between the twospackets.s155sAnother approach based on superposition coding to achieve full rate transmission calledssuperposition coding assisted cooperative multiple access is proposed by Zhiguo ins=-=[109]-=-,where N users each transmitting over N orthogonal channels (frequency, time, orscode) superimposes their own data along with previously received data from the N-1sremaining users. The pre-coding and ...

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...ltiuser detection using superpositionscoding and successive interference cancellation (SIC) receiver can be employed tosmaximise capacity and enable users with different rates to communicate together.=-=[23]-=-sFrequency Time C od e User 1 User 2 User 3 User K Figure 2- 4: Time, frequency and code illustration of the CDMAs2.3.4 Space Division Multiple Access (SDMA)sSDMA [4][24][25] is a high spectral effici...

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...y and codesdimensions of MC-CDMA and MC-DS-CDMA techniques.sFigure 2- 7 : Time, frequency and code dimensions of MC-CDMA and MC-DS-CDMA.s2.3.7 Collaborative Coding Multiple Access (CCMA)sCCMA [32][33]=-=[34]-=-[35][36][37][39][40] is narrowband non-orthogonal MAS which allowssseveral users to transmit simultaneously over a common channel without any subdivision instime, frequency, or code. Hence unlike CDMA...

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...d codesdimensions of MC-CDMA and MC-DS-CDMA techniques.sFigure 2- 7 : Time, frequency and code dimensions of MC-CDMA and MC-DS-CDMA.s2.3.7 Collaborative Coding Multiple Access (CCMA)sCCMA [32][33][34]=-=[35]-=-[36][37][39][40] is narrowband non-orthogonal MAS which allowssseveral users to transmit simultaneously over a common channel without any subdivision instime, frequency, or code. Hence unlike CDMA, CC...

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...desdimensions of MC-CDMA and MC-DS-CDMA techniques.sFigure 2- 7 : Time, frequency and code dimensions of MC-CDMA and MC-DS-CDMA.s2.3.7 Collaborative Coding Multiple Access (CCMA)sCCMA [32][33][34][35]=-=[36]-=-[37][39][40] is narrowband non-orthogonal MAS which allowssseveral users to transmit simultaneously over a common channel without any subdivision instime, frequency, or code. Hence unlike CDMA, CCMA a...

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...�...

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...sions of MC-CDMA and MC-DS-CDMA techniques.sFigure 2- 7 : Time, frequency and code dimensions of MC-CDMA and MC-DS-CDMA.s2.3.7 Collaborative Coding Multiple Access (CCMA)sCCMA [32][33][34][35][36][37]=-=[39]-=-[40] is narrowband non-orthogonal MAS which allowssseveral users to transmit simultaneously over a common channel without any subdivision instime, frequency, or code. Hence unlike CDMA, CCMA allows mu...

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...s of MC-CDMA and MC-DS-CDMA techniques.sFigure 2- 7 : Time, frequency and code dimensions of MC-CDMA and MC-DS-CDMA.s2.3.7 Collaborative Coding Multiple Access (CCMA)sCCMA [32][33][34][35][36][37][39]=-=[40]-=- is narrowband non-orthogonal MAS which allowssseveral users to transmit simultaneously over a common channel without any subdivision instime, frequency, or code. Hence unlike CDMA, CCMA allows multip...

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...fading correlation.sAt the BS antenna separation in the order of 10 wavelengthss52s(1.5m at 2GHz) is required; whilesmore than half a wavelength at the mobile handsets(7.5cm at 2GHz) is required [44] =-=[45]-=-.sn1 nNr h11 h1Nr hNt1 hNtNr 1 Nr H y1 yNr ^ b1 b̂NtbNt x1 xNt b1 DS P DS P Tx Rx 1 Nt Figure 2- 9 Illustration of a SU-MIMO systemsDepending on the average received SNR, SU-MIMO can be used either to...

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...equires the extensively complexs53smultidimensional Viterbi algorithm. Space-time block codes (STBC) on the other handsattains only a diversity order equal to ...

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...ceive-transmit antennas, MIMO attains a linear increase in system capacity in the order ofsminimum number of received /transmit antennas ...

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...d averagestransmit power and SNR at the receiver. This approach is similar to adaptive modulationswhere users vary their modulation and code rate according to channel conditions tosmaximise data rate =-=[70]-=-. But in CMMA, channel inversion rather than water filling is usedsto combine maximising rate with collaborative precoding.s63sEach user utilizes CSI to adjust the phase and power of its signal so tha...

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...y.sMostssynchronization schemes are based on an initial acquisition of reference time between thesBS and users followed by a closed-loop tracking control procedure for maintainingssynchronisation [73]=-=[74]-=-. For CMMA, users transmit in flat fading environment, i.e. theirsrespective signals arrive by a single resolvable path. The delays between arriving paths aresconsidered independent and identically di...

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...usersL=3,sMax(dmin) precodersL=3,sMMSE Linear precodersL=1,sCMMAsL=2,sCMMAsL=3,sCMMA 93sscheme over which 2 independent data streams are sent employing MMSE linear precoders[76] and max mindsprecoder =-=[77]-=- with ML detection and assuming perfect CSI available atsboth transmitter and receiver side. Even with the reduced complexity and feedback overheadscompared to [24-25], CMMA achieves a 0.9 dB gain ove...

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...ly with the channel coherent time is small or/and the number of users areslarge. To overcome this coordination problem, a random access based feedback protocolscalled static splitting was proposed in =-=[91]-=-[92], where only users transmit to the BS duringsthe feedback stage. Here, each data transmission is preceded by a fixed number of minisslots. In each mini slot, users with instantaneous channel gain ...

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...tsthan relay networks in two aspects. Firstly, in its purpose to provide spatial diversity in asfading channel and secondly users in cooperative networks act both as sources and relays.sSendonaris in =-=[99]-=- presented a Code-Division Multiple Access (CDMA) implementation ofsdecode and forward cooperation scheme where two users (each with its own spreadingscode) cooperate with each other over three-bit-in...

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...he expense of doublingsthesbandwidthscompared withsdirect transmission for a givensrate.sTo avoid the use of repetition coding and maintain the same rate as in direct transmission,sHunter proposed in =-=[102]-=- [103] [104] [105] coded cooperation where cooperation issintegrated with channel coding. In coded cooperation, each user will encode K informationsinto B coded bits per block, so that R = K/B. Then t...