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 IEEE Transaction on Communications (place & year if book) Volume no, Vol. 53, No.3, March 2005, page 526 Month & Year, pages Problem being Adapting to time-varying channel conditions and fading to increase addressed 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 / Transmit beamforming and adaptive modulation (transmit power, technology signal constellation, beamforming direction and feedback strategy), used Multiple transmit, one receive antenna, wireless channel is frequency nonselective,

Mathematical Formulate the problem, link with existing works> difficulty in solving techniques original problem analytically, suboptimal formulation> develop the used nested approach> present the numerical results /methodology

Adaptive  Jointly design transmit power, the signal constellation, Modulation 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 IEEE Transaction on Wireless Communications (place & year if book) Volume no, Vol. 3, No.5, September 2004, page 1626 Month & Year, pages Problem being Adapting to time-varying channel conditions and fading to increase addressed 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 / 2-D beamformer (Alamouti data streams are power loaded and technology transmitted along two orthogonal basis beams). Nt transmit and Nr used receive antennas, flat-fading channel, slowly time-varying channel Mathematical Partial CSI: Mean feedback( Models the spatial fading channels as techniques Gaussian random variables with nonzero mean and white covariance ) used /methodology Adaptive  Based on partial CSI (Mean feedback) modulation  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 IEEE Transactions on Wireless Communications (place & year if book) Volume no, Vol.3, No.6, November 2004 Month & Year, pages Problem being Challenge to provide high data rates with high QoS over hostile mobile addressed 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 / Broadband OFDM technology used Mathematical Adaptively select the eigenvectors associated with the relatively large techniques spatial subchannel eigenvalues to generate the beamforming weights at used the mobile and basestations and then dynamically assigns the /methodology 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 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 IEEE Transactions on Wireless Communications (place & year if book) Volume no, Vol.3, No.4, July 2004, page 1285-1294 Month & Year, pages Problem being Channel prediction problems for adaptive modulation addressed 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 / MIMO, Rayleigh fading, multiple transmit, multiple receive, transmit- technology beamformer, MMSE channel predictor based on Pilot Symbol Assisted used Modulation, Independent & identically distributed (iid) Rayleigh fading MIMO channels. Mathematical 1. Present the MMSE predictor techniques 2. analyze the impact of channel prediction error used 3. obtained a closed-form BER expressions for arbitrary number of /methodology receive and transmit antennas 4. 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 IEEE Conference (place & year if book) Volume no, 2004, page 1215-1219 Month & Year, pages Problem being addressed Purpose Propose a new scheme Contributions Propose a combinational scheme of adaptive beamforming and adaptive loading for OFDM System / Least Mean Square algorithm, pre-FFT algorithm, technology used Mathematical  Use frequency-domain adaptive loading to load the bits and techniques transmit power to the individual subcarriers to counter with used frequency selective fading. /methodology  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 2005 Asia-Pacific Conference on Communications, Perth, Western (place & year Australia if book) Volume no, 3-5 October 2005, page 148-152 Month & Year, pages Problem being Effect of variation of PN codes length, modulation types and order addressed 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 / Beamforming in BS, uplink mode, using Least Squares-Constant technology Modulus Algorithm (LS-CMA), Gaussian Wide Sense Stationary used Uncorrelated Scattering Mathematical Investigation done theoretically and using simulations techniques used /methodology 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 IEEE Conference (place & year if book) Volume no, 2003, page 606-610 Month & Year, pages Problem being MS-MS interference (intra and intercell), BS-BS interference addressed 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 / Non-shadowed, log-normal shadowed, Sample Matrix Inversion (SMI) technology used Mathematical Performance metrics used are call dropping probability, Grade of techniques Service, used /methodology 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