MMSE Channel Estimation Research Articles

Performance analysis of OFDM receiver with modified PTS technique

Modified partial transmit sequence PTS technique with adjacent partitioning and four phase factors is implemented to enhance the PAPR performance of OFDM system and its PAPR reduction performance is evaluated in terms of the complementary cumulative distribution function CCDF. A multipath fading environment is considered and the performance of the OFDM receiver is evaluated using least square LS and minimum mean square error MMSE channel estimation methods. The performance of the receiver is evaluated in terms of mean square error MSE and bit error rate BER. The performance of the OFDM receiver is enhanced with PAPR reduction.

Performance Evaluation of Channel Estimation Techniques in OFDM based Mobile Wireless System

In this modern wireless technology Multicarrier communication is one of the more suitable and reliable communication technique. Orthogonal Frequency Division Multiplexing (OFDM) is used as modulation technique in multicarrier communication. The present paper gives an overview of OFDM and the various Channel Estimation techniques used in OFDM. The results implemented in MATLAB gives the performance of LS and the MMSE channel estimators for an OFDM system based on the parameters of BER and MSE. Paper also describes the Delayed feedback MIMO OFDM channel estimation performance of LS and LMMSE and DFT based channel estimation technique for LS-linear and MMSE estimator. BPSK and 16-QAM modulation techniques are used.

On the optimality of training signals for MMSE channel estimation in MIMO-OFDM systems

In this paper, we investigate the optimality of training signals for linear minimum mean square error (LMMSE) channel estimation in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) with frequency-selective fading channels. This is a very challenging problem due to its mathematical intractability and has not been analytically solved in the literature. Using the Lagrange multiplier method, we derive the optimality conditions for training signal design. Important findings revealed on optimal training signals are twofold: (i) the energies of the training signals on each subcarrier are equal, and (ii) on each subcarrier, the training signals transmitted from the different antennas are orthogonal and of equal energy. We verify that our results are in line with the design principles that have been derived in single-carrier MIMO systems. Two types of optimal training signal examples that satisfy the optimality conditions are presented for practical implementations in MIMO-OFDM systems. Simulation results show that the training signals based on the optimality conditions outperform other non-optimal training signals in terms of channel estimation performance.

Convergence analysis of a joint signal‐to‐noise ratio and channel estimator for frequency selective channels in orthogonal frequency division multiplexing context

In this article, the authors study the convergence of an iterative algorithm for the joint estimation of the signal-to-noise ratio (SNR) and the transmission channel in orthogonal frequency division multiplexing context. At each step of the algorithm, the authors use the minimum-mean-square error (MMSE)-based SNR estimation, which feeds the linear MMSE channel estimation. Reciprocally, this efficient channel estimation is used to perform the SNR estimation. The authors provide a proof of convergence of the algorithm to a single value. Furthermore, we derive an accurate approximation of the bias of the estimation. Simulations show that the algorithm converges quickly and verifies the theoretical results. They also show the efficiency of both SNR and channel estimation. By comparing with the existing methods, the authors show that the tradeoff between the number of required pilots in the preamble and the performance of the SNR estimation were improved. Furthermore, for a fixed bit error rate, the SNR gap between the proposed channel estimation and the perfect one is <0.5 dB.

Uplink Sum-Rate Analysis of Massive MIMO System with Pilot Contamination and CSI Delay

We consider multi-cell multi-user massive MIMO system under correlated Rayleigh fading channels. Taking pilot contamination and CSI delay into consideration, we derive the equivalent channel model with MMSE channel estimation and one-tap prediction. Employing this equivalent channel model, the lower bound of the uplink sum-rate is derived, and its asymptotical performance is studied when the base station antenna number goes without bound. We find that if we schedule the $$k$$ k -th user of all cells who have the same prediction coefficient, the uplink sum-rate is the same as the one with no CSI delay when the number of BS antennas goes without bound at a much greater rate than the number of users. Simulation results show that the asymptotic approximation has good performance for large $$M$$ M , and suggest that large antenna array can compensate for the decay due to CSI delay. Simulation results also verify our guess that CSI delay does not necessarilly decrease the uplink sum-rate due to the impact of pilot contamination.

User Capacity Scaling Laws of Multi-user Fading Channels in the Presence of MMSE Channel Estimators

Considering development of delay-sensitive applications in wireless communications and cellular networks along with lack of system resources and environmental factors including fading and noise all together make it impossible for all users to be active and to achieve quality of service requirements simultaneously. To analyze wireless systems performance, user capacity is defined as the maximum number of users that can be activated at the same time. In order to obtain user capacity scaling laws, channel distribution information is required and channel gains can be estimated by different channel estimators such as minimum mean square error estimators. In this paper, estimated channel gains are substituted for true channel gains and effects of imperfect channel estimation errors on the user capacity scaling laws are analyzed. It is shown that the user capacity scales double logarithmically and there is a gap depending on channel estimators accuracy between the lower and upper bounds. Moreover, assuming estimated channels for different users are independent and identically distributed, it is shown that the user capacity scaling laws are asymptotically tight.

Low-Complexity MMSE Channel Estimator for MB-OFDM UWB Systems

Low-Complexity MMSE Channel Estimator for MB-OFDM UWB Systems

An Improved Multicell MMSE Channel Estimation in a Massive MIMO System

Massive MIMO is a promising technology to improve both the spectrum efficiency and the energy efficiency. The key problem that impacts the throughput of a massive MIMO system is the pilot contamination due to the nonorthogonality of the pilot sequences in different cells. Conventional channel estimation schemes cannot mitigate this problem effectively, and the computational complexity is increasingly becoming larger in views of the large number of antennas employed in a massive MIMO system. Furthermore, the channel estimation is always carried out with some ideal assumptions such as the complete knowledge of large-scale fading. In this paper, a new channel estimation scheme is proposed by utilizing interference cancellation and joint processing. Highly interfering users in neighboring cells are identified based on the estimation of large-scale fading and then included in the joint channel processing; this achieves a compromise between the effectiveness and efficiency of the channel estimation at a reasonable computational cost, and leads to an improvement in the overall system performance. Simulation results are provided to demonstrate the effectiveness of the proposed scheme.

A Comparative Performance Study of OFDM System with the Implementation of Comb Pilot-Based MMSE Channel Estimation

A Comparative Performance Study of OFDM System with the Implementation of Comb Pilot-Based MMSE Channel Estimation

도플러 대역폭이 채널 추정의 성능에 미치는 영향

본 연구에서는 도플러 대역폭이 채널 사운딩에 미치는 영향을 고려한다. 이를 위해 먼저 수학적인 공식을 전개한 후에 단순한 상관기와 MMSE를 비교한다. 시간 변화의 영향을 평가하기 위하여 MMSE와 상관기의 성능은 SISO 환경하에서 다양한 도플러 대역폭 값을 적용하여 분석한다. 시뮬레이션 결과를 통하여 <TEX>$f_dT$</TEX> 값이 증가할수록 MMSE와 상관기의 성능은 더 열화되며 MMSE의 성능은 상관기에 비해 향상됨을 보인다 또한 정확한 채널 정보가 알려져 있지 않을 경우의 성능 열화에 대해서도 고려한다. 채널 정보의 부정확도가 낮을 경우에는 여전히MMSE의 성능이 좋지만 채널 정보의 부정확성이 커질수록 상관기의 성능이 더 좋아짐을 보인다. 본 연구는 기존에 직관적으로 시행해 왔던 MMSE와 성관기의 성능 분석을 위한 시뮬레이션에 추가적으로 수학적인 접근법을 제공하여 그 응용분야를 넓혀 갈 수 있음을 보인다. In this work, we consider the effect of doppler bandwidth on the performance of channel sounding. We develop the mathematical formulation of the problem and compare the MMSE channel estimator to the simple correlator. Examples of the performance of the MMSE and correlator estimators are presented for the single-input single-output (SISO) case with various values of Doppler bandwidth to assess the impact of time variation. The results show that as the <TEX>$f_dT$</TEX> product increases the performance of both the MMSE and correlator estimates gets worse, and that the performance of the MMSE estimator improves relative to the correlator.We also consider case that the exact statistics of the channel are unknown It is shown that when the mismatch is not too large, the MMSE estimator with mismatch still does better than the simple correlator, but if the mismatch is large, then the correlator can do better.

BER Analysis of OFDM Receiver Using MMSE Channel Estimation Method with PTS for Different Subblocks

BER Analysis of OFDM Receiver Using MMSE Channel Estimation Method with PTS for Different Subblocks

Soft‐output MMSE V‐BLAST receiver with MMSE channel estimation under correlated Rician fading MIMO channels

ABSTRACTFor wireless multiple‐input multiple‐output (MIMO) communications systems, both channel estimation error and spatial channel correlation should be considered when designing an effective signal detection system. In this paper, we propose a new soft‐output MMSE based Vertical Bell Laboratories Layered Space‐Time (V‐BLAST) receiver for spatially‐correlated Rician fading MIMO channels. In this novel receiver, not only the channel estimation errors and channel correlation but also the residual interference cancellation errors are taken into consideration in the computation of the MMSE filter and the log‐likelihood ratio (LLR) of each coded bit. More importantly, our proposed receiver generalizes all existing soft‐output MMSE V‐BLAST receivers, in the sense that, previously proposed soft‐output MMSE V‐BLAST receivers can be derived as the reduced forms of our receiver when the above three considered factors are partially or fully simplified. Simulation results show that the proposed soft‐output MMSE V‐BLAST receiver outperforms the existing receivers with a considerable gain in terms of bit‐error‐rate (BER) performance. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Effect of MMSE Channel Estimation on BER Performance of Orthogonal Space-Time Block Codes in Rayleigh Fading Channels

We present a simple closed-form expression for the BER of orthogonal space-time block codes (OSTBCs) with MMSE channel estimation, assuming PAM and QAM constellations and flat Rayleigh block fading. The BER expression is exact for a certain class of OSTBCs, and provides a very accurate approximation for other OSTBCs.

Optimisation of the pilot-to-data power ratio in the wireless MIMO-OFDM system with low-complexity MMSE channel estimation

Multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) communication systems are currently being viewed as a main candidate for the next generation broadband wireless access interfaces providing high throughput. However, a considerable potential gain in spectral efficiency is challenged by the receiver’s ability of accurate data symbol identification at the output of the radio channel. Performance of the MIMO detectors strongly depends on both the received signal-to-noise power ratio (SNR) and the retrieved channel state information (CSI), which can be obtained using the channel estimation techniques relying on pilot symbol transmission on the dedicated subcarriers. Necessity to improve channel estimation and detection performance concurrently leads to the dilemma of the optimal power assignment to the data and pilot subcarriers as these are the conflicting requirements under the total transmit power constraint. We derive an analytical solution of the described problem in the form of weak and tight upper bounds on the pilot-to-data power ratio (PDR) given the system design parameters (number of subcarriers, number of pilots, number of transmit antennas, model order of the channel response, SNR). The resultant PDR equations can be applied to OFDM systems with arbitrary arrangement of the pilot subcarriers operating in an arbitrary multipath channel, not just limited to the equispaced optimal pilot pattern and the channel with the uniform sample-spaced power-delay profile as studied in the previous works. In an adaptive system, which is capable to adjust transmit signal configuration (e.g., block length, number of pilot subcarriers or antennas) according to the established channel conditions, an optimal parameter tuning is desirable for each operational mode. The closed-form PDR expressions and their analysis presented in this work are designated to alleviate the challenging task of the on-the-fly system optimisation as they represent relatively simple functional relationships.

Delay-spread estimation using cyclic-prefix in wireless OFDM systems

A novel cyclic-prefix based delay-spread estimation technique for wireless OFDM systems is proposed. In particular, the authors propose a technique for estimating the delays and powers of multipath components when the channel is sparse, i.e. a few strong multipaths distantly spaced in time, and a technique for estimating the RMS delay-spread when the channel has a large number of sample-spaced multipath components. The proposed techniques are based on a multiple-argument correlation function which exhibits change of gradient according to the delay path arrival pattern, i.e delay times and powers. Numerical results demonstrate the accuracy of the proposed techniques in estimating the relative timing and the power of delay paths for a sparse multipath channel, and the RMS delay-spread for a sample-spaced multipath channel. Moreover, the RMS delay-spread estimation can be used adaptively to operate the MMSE channel estimation process in the OFDM receiver at near optimum.

A new family of soft-output adaptive receivers exploiting nonlinear mmse estimates for TDMA-based wireless links

Decision-directed adaptive receivers suffer performance degradation on time varying and intersymbol interference-impaired links because of two major problems: the use of predicted channel estimates due to the unavoidable decision delay of any detector, and the unreliability of hard decisions used for channel estimation and tracking. It is shown here that combining a recursive nonlinear symbol estimator with a channel estimator with a low prediction order may alleviate this performance degradation. In particular, it is here proposed to employ the nonlinear minimum mean-square error (NL-MMSE) filtered and fixed-lag smoothed estimates of the transmitted symbols in place of the usual hard decisions for channel estimation and tracking. It is also shown that these NL-MMSE estimates can be recursively computed on the basis of a linear transformation of the vector of the a posteriori probabilities (APPs) of the states of the channel. This approach allows the prediction order of the channel estimates to be limited and, at the same time, limits the performance degradation due to erroneous hard decisions. Another result presented here is that the use of NL-MMSE estimates in place of hard decisions is not based on mere intuition only, but is a straightforward consequence of the statement of the problem of MMSE channel estimation when the overly optimistic assumption of correct decisions is dropped. On the basis of this novel approach, a new family of soft-output adaptive receivers is presented for time-division multiple-access-based radio communications. The proposed family of adaptive receivers is based on an APP-computer and exploits the APPs for both channel estimation and detection. The versatility of the APPs ensures that the architecture of the proposed receiver is flexible, so that several estimators and detectors can be embedded in it.

Pilot-Symbol-Assisted Channel Estimation for Space-Time Coded OFDM Systems

Space-time coded orthogonal frequency division multiplexing (OFDM) transmitter diversity techniques have been shown to provide an efficient means of achieving near optimal diversity gain in frequency-selective fading channels. For these systems, knowledge of the channel parameters is required at the receivers for diversity combining and decoding. In this paper, we propose a low complexity, bandwidth efficient, pilot-symbol-assisted (PSA) channel estimator for multiple transmitter OFDM systems. The pilot symbols are constructed to be nonoverlapping in frequency to allow simultaneous sounding of the multiple channels. The time-varying channel responses are tracked by interpolating a set of estimates obtained through periodically transmitted pilot symbols. Simulations are used to verify the effectiveness of the propsed estimator and to examine its limitations. It is also shown decision-directed minimum mean square error MMSE channel estimator for OFDM transmitter diversity systems.