LITERATURE REVIEW (review/experimental/analytical/Case Study/Technical note/ others)

Title / Adaptive Modulation & MIMO Coding for Broadband Wireless Data Networks
Author(s) / Severine Catreux, Vinko Erceg, David Gesbert, Robert W. Health
Publication (place & year if book) / IEEE Communication Magazine
Volume no, Month & Year, pages / June 2002, page 108
Problem being addressed / Link adaptation techniques in broadband wireless networks with multiple signaling dimensions.
Purpose / Give overview of challenges and promises of link adaptation in future broadband wireless networks
Contributions / Suggest guidelines to help in the design of robust, complexity/cost-effective algorithms for future wireless networks
Mathematical techniques used /methodology
Assumptions
Challenges/ issues / 1.  Determination of Adaptation Thresholds
2.  Adaptation rate: tradeoff between performance gain and amount of resource allocated.(fast adaptation increases the number of mode-change messages increase the consumption of bandwidth and time)
Conclusions
Critique
Title / Multiantenna Adaptive Modulation with Beamforming Based on Bandwidth-Constrained Feedback
Author(s) / Pengfei Xia, Shengli Zhou, Georgios B. Giannakis
Publication (place & year if book) / IEEE Transaction on Communications
Volume no, Month & Year, pages / Vol. 53, No.3, March 2005, page 526
Problem being addressed / Adapting to time-varying channel conditions and fading to increase rate, with rate-limited feedback
Purpose / Investigate adaptive modulation system based on transmit beamforming with rate-limited feedback. Jointly design the feedback strategy and transmission parameters for rate-limited feedback
Contributions / Proposed a nested iterative approach that yield a practical design of the adaptive transmission and feedback strategy
System / technology used / Transmit beamforming and adaptive modulation (transmit power, signal constellation, beamforming direction and feedback strategy),
Multiple transmit, one receive antenna,
Mathematical techniques used /methodology / Formulate the problem, link with existing works> difficulty in solving original problem analytically, suboptimal formulation> develop the nested approach> present the numerical results
Assumptions / Channel do not vary within block, independent identically distributed channel coefficients, Perfect CSI at receiver, Feedback channel is error free, delay free
Key Results / Throughput enhancement (considerable improvement in transmission rate, as the number of feedback bits increases)
Conclusions / A finite number of feedback bits can improve the overall performance considerably
Critique
Title / Adaptive Modulation for Multiantenna Transmissions with Channel Mean Feedback
Author(s) / Shengli Zhou, Georgios B. Giannakis
Publication (place & year if book) / IEEE Transaction on Wireless Communications
Volume no, Month & Year, pages / Vol. 3, No.5, September 2004, page 1626
Problem being addressed / Adapting to time-varying channel conditions and fading to increase rate, CSI imperfections (estimation errors & feedback delays)
Purpose / ·  To design adaptive modulation scheme for multiantenna transmissions with channel mean feedback.
·  Investigate adaptive trellis-coded multiantenna modulation
Contributions / Proposed a transmitter based on two dimensional beamformer that optimally adapts the basis beams, the power allocation between the two beams, and signal constellation to maximize the transmission rate, while maintaining the target BER
System / technology used / 2-D beamformer (Alamouti data streams are power loaded and transmitted along two orthogonal basis beams). Nt transmit and Nr receive antennas, flat-fading channel, slowly time-varying channel
Mathematical techniques used /methodology / Models the spatial fading channels as Gaussian random variables with nonzero mean and white covariance,
Assumptions
Key Results
Conclusions / ·  The result shows rate improvement, illustrate an interesting tradeoff emerges between feedback quality and hardware complexity
·  Relaxing the receiver complexity constraint, adaptive modulation based on spatial multiplexing schemes is an interesting future research topic
Critique
Title / Adaptive beamforming algorithm for OFDM Systems with Antenna System
Author(s) / Chan Kyu Kim, Kwangchun Lee, and Yong Soo Cho
Publication (place & year if book) / IEEE Transaction on Consumer Electronics
Volume no, Month & Year, pages / Vol. 46, No.4, November 2000, page 1052
Problem being addressed / Problem of designing a new adaptive beamforming algorithm for OFDM due to the nature of OFDM system utilizing IFFT/FFT operation for modulation/demodulation
Purpose / Propose a new adaptive beamforming technique
Contributions / Proposed a new adaptive beamforming technique for OFDM
System / technology used / OFDM, adaptive linear array antenna, M users, 16 QAM, OFDM block size: 32, distance between adjacent elements: lambda/2,
Mathematical techniques used /methodology / Derive the proposed algorithm by calculating the error signals between pilot symbols and the corresponding received signals in frequency domain, transforming the error signals into time-domain error signal, updating the filter coefficients of adaptive beamformer in the time domain in the direction of minimizing the MSE. Investigate the convergence behavior and performance improvement by computer simulation
Assumptions
Key Results / Convergence behavior as function of step size and number of pilot symbols , BER performance as a function of number of antenna arrays
Conclusions / Although it requires signal processing in both domain, it has similar properties to the conventional beamforming algorithms (BER increase with number of array elements, convergence faster as step size increase and number of pilot symbol increases.
Critique
Title / A Novel Adaptive Beamforming Algorithm for a Smart Antenna System in a CDMA Mobile Communication Environment
Author(s) / Seungwon Choi and Donghee Shim
Publication (place & year if book) / IEEE Transaction on Vehicular Technology
Volume no, Month & Year, pages / Vol.49, No.5, September 2000
Problem being addressed / Problem of designing an adaptive antenna array using second order statistics of the received signal
Purpose / Find a weight vector that provides an appropriate beam pattern to each subscriber in a given cell/sector, the weight vector computed by the algorithm produces a suboptimal beampattern that generates its maximum gain along the direction of the target user
Contributions / A new simpler adaptive beamforming algorithm with minimal loss of accuracy
System / technology used / CDMA receiving base station, M beamforming to handle M subscribers in a cell,
Mathematical techniques used /methodology / Utilize Lagrange formula, to compute weight vector of the array in iterative manner, derived analytically the required condition on the adaptive gain for the algorithm to converge
Assumptions
Key Results / The proposed algorithm provide remarkable improvement in reliability & capacity. Performance becomes more when combine with Rake receiver
Conclusions / Main attractive feature: simplicity. Does not require training symbols, mathematically valid regardless of the number of antenna elements and that of interferers, the signal coherence does not affect the performance or complexity of the proposed algorithm
Critique
Title / Performance of Wireless MC-CDMA System with Antenna Array in a Fading Channel: Reverse Link
Author(s) / Chan Kyu Kim, Yong Soo Cho
Publication (place & year if book) / IEEE Transaction on Communications
Volume no, Month & Year, pages / Vol. 48, No.8, August 2000, page 1257
Problem being addressed / Multiuser interference, fading channel
Purpose / Propose a new system
Contributions / Propose a MC-CDMA system employing an antenna array at the base station, and analyze the performance in fading channel
System / technology used / Reverse link
Mathematical techniques used /methodology / The optimal beamformer for the proposed MC-CDMA system is constructed using non-direction-finding technique similar to the code-filtering technique, derived in the reverse link using preprocessing array covariance matrix and post-processing covariance matrix. Analytic formula of error probability was derived
Assumptions / Exact synchronization in timing and frequency, no Doppler shift and EGC,
Key Results / BER of MC-CDMA approach better than DS-CDMA
Increase in system capacity as number of antenna elements increase
Conclusions / When the non-direction-finding techniques is used for antenna array in MC-CDMA and DS-CDMA, the performance of MC-CDMA is shown to be better than DS-CDMA
Confirmed by computer simulation that analytic formula approximate real situation when number of user is large and substantial increase in system capacity is possible by incorporating antenna array at base station
Critique
Title / Beamforming in Combination with Space-Time Diversity for Broadband OFDM Systems
Author(s) / Armin Dammann, Ronald Raulefs, Stefan Kaiser
Publication (place & year if book) / IEEE
Volume no, Month & Year, pages / 2002, page 165
Problem being addressed / Multipath fading problem.
Purpose / Propose a novel approach : Combine space-time diversity with Beamforming
Contributions / The proposed technique modifies the transmission signal in a way that the received signal can be detected more reliably by the receiver than in conventional techniques. The negative impact of fading is minimized and therefore the needed transmission power is reduced, implicitly minimizing the cell interference.
System, technology used / Broadband OFDM, beamforming, space-time diversity: cyclic delay diversity (CDD), Maximum Ratio Combining (MRC)
Mathematical techniques used /methodology / Simulation, compare BER of different beamforming scenarios and CDD in Rayleigh fading channel. MRC also taken into account in performance analysis
Assumptions
Key Results
Conclusions / In comparisons to conventional schemes with adaptive antennas the novel approach alters the spectrum and error distribution at the receiver, and therefore performs much better for the used OFDM system
Critique
Title / Power Allocation for OFDM using adaptive beamforming over Wireless Network
Author(s) / Masoud Olfat, Farrokh Rashid-Farrokhi, K.J.Ray Liu
Publication (place & year if book) / IEEE Transactions on Communications
Volume no, Month & Year, pages / Vol.53, No.3, March 2005
Problem being addressed / In OFDM, overall BER is dominated by the performance of worst SNR subcarrier.
Purpose / Present the performance of of multiuser network using OFDM, combined with power control and adaptive beamforming for uplink transmission.
Contributions / Propose joint time-domain beamforming and power control(less complexity than frequency domain), also extended to COFDM
System / technology used / Power control, uplink, multiuser, OFDM,
Mathematical techniques used /methodology / Transmit powers and beamforming weight vectors at each subcarrier are updated jointly, using iterative algorithm that converges to the optimal solution for the entire network.
Assumptions / Fixed modulation for all subcarriers,
Key Results
Conclusions / SINR at all subcarriers of all mobiles could be at least equal to a target value, while the total network power is minimized.
Critique
Title / Dynamic Spatial Subchannel Allocation with Adaptive Beamforming for MIMO/OFDM Systems
Author(s) / Ya-Han Pan, Khaled ben Letaief, Zhigang Cao
Publication (place & year if book) / IEEE Transactions on Wireless Communications
Volume no, Month & Year, pages / Vol.3, No.6, November 2004
Problem being addressed / Challenge to provide high data rates with high QoS over hostile mobile environments with limited spectrum and ISI.
Purpose / Propose a new technique
Contributions / 1.  Propose a dynamic spatial subchannel allocation with adaptive beamforming for broadband OFDM wireless transmission system
2.  Considered the performance of the proposed system combine with adaptive modulation
System / technology used / Broadband OFDM
Mathematical techniques used /methodology / Adaptively select the eigenvectors associated with the relatively large spatial subchannel eigenvalues to generate the beamforming weights at the mobile and basestations and then dynamically assigns the corresponding best spatial subchannels to transmit the OFDM block symbols.
Assumptions
Key Results / 1.  proposed system can achieve better performance than an adaptive antenna-arrays-based OFDM system without dynamic spatial subchannel allocation over multipath fading channels
2.  proposed system is far less susceptible to feedback delay in rapid time-varying channels and a little more sensitive to channel estimation errors than conventional adaptive antenna-arrays-based OFDM systems.
Conclusions / The proposed system could be prove to be an effective scheme for providing significant increases in system’s capacity and bandwidth efficicency as well as improvement in QoS
Critique
Title / Adaptive Interference Suppression in Multiuser Wireless OFDM System using Antenna Arrays
Author(s) / IEEE Transactions on Signal Processing
Publication (place & year if book)
Volume no, Month & Year, pages / Vol.47, No.12, December 1999, page 3381
Problem being addressed / Mitigating fading and interference in wireless OFDM, ICI, CCI
Purpose / Propose a new technique
Contributions / Propose array combining algorithm 1. optimum array combining using the maximum SINR criterion used for slowly time-varying channel. 2. alternative two stage adaptive array architecture for fast time-varying channel
System / technology used / At base station, synchronous uplink OFDM reception based on loop-timing.
Mathematical techniques used /methodology
Assumptions
Key Results
Conclusions / 1. for fast fading and frequency offset induced ICI spatial diversity using MRC is most effective 2. for slowly fading pilot-assisted array combining provides superior performance compared with MRC when the number of dominant interferers is smaller than the number of elements
Critique
Title / Transmit Beamforming Design in Wide Angle Spread Scenarios for B3G MC-CDMA Systems
Author(s) / Santiago Zazo, Ivana Raos, Spain
Publication (place & year if book) / 2004 IEEE 5th Workshop on Signal Processing Advances in Wireless Communications
Volume no, Month & Year, pages / 2004, page 248
Problem being addressed / Designing transmit beamforming for beyond 3G, with large angle spread and wideband transmission
Purpose / Propose a new technique
Contributions / Present an alternative technique with partial channel knowledge, based on the spatial autocorrelation function estimated in uplink that outperforms standard beamforming techniques
System / technology used / Transmit downlink, wideband MC-CDMA,
Mathematical techniques used /methodology / simulation
Assumptions
Key Results
Conclusions / The scheme is shown to provide competitive performance to be used in B3G system fully compatible with TDD/FDD in fast fading
Critique
Title / Beam-forming for MC-CDMA Systems
Author(s) / R. Venkatasubramanian, Jiann-An Tsai, R. Michael Buehrer
Publication (place & year if book) / The 2002 45th Midwest Symposium on Circuit & Systems (MWSCAS-2002)
Volume no, Month & Year, pages / Vol. 3, August 2002, page III-441 – III-444
Problem being addressed
Purpose / Investigate the use of adaptive antenna arrays for MC-CDMA system in interference-dominated environment
Contributions / 1. Evaluate the BER performance of the beamforming algorithm under different channel conditions: flat, frequency selective, low & high angle spread, low & high Doppler spreads.
2. Present 2 methods of beamforming: frequency domain & time domain.
3. Investigate MMSE detector combined with beamforming
4. channel estimation using Cubic spline interpolator in time domain