Literature Review Summary (Combining Adaptive Modulation and Adaptive Beamforming )

Literature Review summary (Combining “adaptive modulation” and “adaptive beamforming”)

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, wireless channel is frequency nonselective,
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
Adaptive Modulation /

Jointly design transmit power, the signal constellation, beamforming direction and feedback strategy
Subject to average BER, and average transmit-power constraint
B feedback bits per block, decides a feedback index n  {1, 2, …, N}, N= 2B
Corresponding to each index n, transmitter will select the transmission mode Mn = (Mn, Pn, Wn)
Mn= signal constellation size
Pn= transmit power
Wn=beamsteering vector
For signal constellation, consider 2 case : continuous rate & discrete rate
Continuous-rate: Mn= 2 bn , where bn  0 is arbitrary real number
Discrete-rate: Mn= 22, 24, 26, …;, bn are even integers, corresponding to square M-QAM constellation
Mn=0 : no data transmission
Goal: maximize transmission rate, subject to certain performance and power constraints
Nested iterative approach developed to yield suboptimal yet practical design for continuous rate case
Discrete rate designed based on continuous rate

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 / Partial CSI: Mean feedback( Models the spatial fading channels as Gaussian random variables with nonzero mean and white covariance )
Adaptive modulation /

Based on partial CSI (Mean feedback)
Two dimensional beamformer
Transmitter optimally adapts the basis beams, the power allocation between to beams, and signal constellation, to maximizes the transmission rate, while maintaining the target BER

Assumptions
Key Results /

rate improvement
adaptive multiantenna modulation turns out to be less sensitive to channel imperfections, compared to single antenna counterpart

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 / 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 /

Propose a dynamic spatial subchannel allocation with adaptive beamforming for broadband OFDM wireless transmission system
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 /

proposed system can achieve better performance than an adaptive antenna-arrays-based OFDM system without dynamic spatial subchannel allocation over multipath fading channels
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 / How Accurate Channel Prediction Needs to be for Transmit- Beamforming with Adaptive Modulation over Rayleigh MIMO Channels?
Author(s) / Shengli Zhou, Georgios B. Giannakis
Publication (place & year if book) / IEEE Transactions on Wireless Communications
Volume no, Month & Year, pages / Vol.3, No.4, July 2004, page 1285-1294
Problem being addressed / Channel prediction problems for adaptive modulation
Purpose / Analyze the impact of channel predictor error on the BER performance of a transmit beamformer with adaptive modulation that treats the predicted channel is perfect.
Contributions / Reveal the critical value of the normalized prediction error, below which the predicted channels can be treated as perfect by the adaptive modulator, otherwise, explicit consideration of the channel imperfection must be accounted for at the transmitter
System / technology used / MIMO, Rayleigh fading, multiple transmit, multiple receive, transmit-beamformer, MMSE channel predictor based on Pilot Symbol Assisted Modulation, Independent & identically distributed (iid) Rayleigh fading MIMO channels.
Mathematical techniques used /methodology /

Present the MMSE predictor
analyze the impact of channel prediction error
obtained a closed-form BER expressions for arbitrary number of receive and transmit antennas
derive simple closed-form expressions when transmit and/or receive antennas are less or equal to 2

Assumptions
Key Results
Conclusions /

BER performance of the adaptive transmit-beamforming based system depends on various system parameters only through a single variable, the normalized channel prediction error.
When the error is below a certain critical value, the predicted channels can be treated as perfect by the adaptive modulator

Critique
Title / Combination of Adaptive Beamforming & Adaptive Loading for OFDM Packet Transmission
Author(s) / Ming Lei, Hiroshi Harada, Hiromitsu Wakana, Ping Zhang
Publication (place & year if book) / IEEE Conference
Volume no, Month & Year, pages / 2004, page 1215-1219
Problem being addressed
Purpose / Propose a new scheme
Contributions / Propose a combinational scheme of adaptive beamforming and adaptive loading for OFDM
System / technology used / Least Mean Square algorithm, pre-FFT algorithm,
Mathematical techniques used /methodology /

Use frequency-domain adaptive loading to load the bits and transmit power to the individual subcarriers to counter with frequency selective fading.
Investigate 2 adaptive beamforming schemes based on LMS algorithm used to estimate the array weight, difference in either using time or frequency domain pilot vector. Both are based on pre-FFT combining (lower complexity than post-FFT).

Assumptions
Key Results / Beamforming scheme based on frequency domain pilot has marginal performance gain while the one based on time-domain pilot has comparatively low complexity.
Conclusions / The combinational scheme based on the adaptive beamforming & adaptive loading is very effective in improving the performance of OFDM packet transmission (decreasing PER)
Critique
Title / Effect of modifying Signal parameters on the Beamforming Performance in CDMA Mobile Communications
Author(s) / B. Banitalebi, M. Karimi, M. Kamarei, G. Dadashsadeh (Iranian)
Publication (place & year if book) / 2005 Asia-Pacific Conference on Communications, Perth, Western Australia
Volume no, Month & Year, pages / 3-5 October 2005, page 148-152
Problem being addressed / Effect of variation of PN codes length, modulation types and order change the beamformer performance
Purpose / Analyze the effects of variation of the signal properties on the performance of the beamformer for two simple and mostly used modulation techniques
Contributions
System / technology used / Beamforming in BS, uplink mode, using Least Squares-Constant Modulus Algorithm (LS-CMA), Gaussian Wide Sense Stationary Uncorrelated Scattering
Mathematical techniques used /methodology / Investigation done theoretically and using simulations
Assumptions
Key Results /

When the number of users is constant, increasing the code length can efficiently improve the performance of the beamformer
Increasing the modulation order to achieve higher data transmission rates causes some degradation in the output SER bit it is not very serious
Signal interference ratio has no significant effect on the beamformer performance
Using QAM modulation which uses both phase and amplitude to separate different symbols from each other gives smaller values of SER than PSK modulation

Conclusions / The parameters have different effects on the beamformer performance
Critique
Title / On the Networking Performance of UTRA-like TDD and FDD CDMA Systems Using Adaptive Modulation and Adaptive Beamforming
Author(s) / Song Ni, Jonathan S. Blogh, Lajos Hanzo
Publication (place & year if book) / IEEE Conference
Volume no, Month & Year, pages / 2003, page 606-610
Problem being addressed / MS-MS interference (intra and intercell), BS-BS interference
Purpose
Contributions /

Characterize the capacity of an adaptive modulation assisted, beam steering aided TDD/CDMA system.
Studies the achievable network performance by simulation and compares it to that of FDD/UTRA system

System / technology used / Non-shadowed, log-normal shadowed, Sample Matrix Inversion (SMI)
Mathematical techniques used /methodology / Performance metrics used are call dropping probability, Grade of Service,
Assumptions / The base station is equipped with the Minimum Mean Squared Error Block Decision Feedback Equaliser based MUD
Key Results
Conclusions / The employment of adaptive arrays in conjunction with AQAM limited the detrimental effects of co-channel interference and resulted in performance improvements both in terms of achievable call quality and the system’s capacity
Critique