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Channel estimation schemes for OFDM relay-assisted systems

Neves, Darlene; Ribeiro, Carlos; Silva, Adão; Gameiro, Atílio
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
67.627227%
The aim of this paper is to adapt and evaluate the performance of two classical pilot-aided channel estimation schemes designed for OFDM systems: least square and minimum mean square error, in a relay-assisted scenario. We consider the Amplify-and-Forward, which is the simplest relay protocol for cooperative systems. Also, we consider the use of a single antenna at all the terminals: base station, user terminal and relay node. In our scenario, it is assumed that some of the user terminals deployed in a certain area could act as relaying-able terminals for the communications of other users. In this communication we show that the classical channel estimation techniques designed for conventional wireless communications can be extended for relay-assisted based systems under some modifications. © 2009 IEEE.; European CODIV project (ref. FP7-ICT-2007-215477); Portuguese Foundation for Science and Technology (FCT)

Robust channel estimation for broadband satellite communications

Balseiro, Filipe
Fonte: Instituto Universitário de Lisboa Publicador: Instituto Universitário de Lisboa
Tipo: Dissertação de Mestrado
Publicado em 11/08/2011 Português
Relevância na Pesquisa
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Mestrado em Engenharia de Telecomunicações e Informática; Com o rápido crescimento das comunicações digitais nos últimos anos, a necessidade de transmissões de dados a alta velocidade aumentou significativamente. Além disso, espera-se que os futuros sistemas sem fios sejam capazes de suportar uma ampla gama de serviços que incluam vídeo, dados e voz. Orthogonal Frequency Division Multiplexing (OFDM) é um candidato promissor para conseguir taxas de transmissão elevadas em ambientes móveis, devido à sua resistência à Inter Symbol Interference (ISI), que consiste num problema comum em comunicações de dados de alta de velocidade. No OFDM, a modulação pode ser diferencial ou coerente. No caso da modulação diferencial não existe necessidade de obter estimação do canal mas o seu desempenho é inferior relativamente ao sistema coerente. A modulação coerente exige estimação de canal que proporciona um melhor desempenho mas apresenta uma estrutura do receptor mais complexa. Na dissertação vão ser estudadas estas duas técnicas: Pilot Symbol Assisted Modulation (PSAM) e pilotos implícitos. No primeiro caso os pilotos transmitidos são multiplexados com os dados, enquanto na segunda situação os pilotos são alocados em posições juntamente com os dados. Nesta dissertação...

Optimum-Weighted RLS Channel Estimation for Rapid Fading MIMO Channels

Koike-Akino, Toshiaki
Fonte: Institute of Electrical and Electronics Engineers Publicador: Institute of Electrical and Electronics Engineers
Português
Relevância na Pesquisa
67.683247%
This paper investigates on an accurate channel estimation scheme for fast fading channels in multiple-input multiple-output (MIMO) mobile communications. A high-order exponential-weighted recursive least-squares (EW-RLS) method has been known as a good channel estimation scheme in rapid fading. however, there exists a drawback that we need to properly adjust the estimation order according to the channel environment. In this paper, we theoretically derive an optimum-weighted LS (OW-LS) channel estimation based on the statistical knowledge of the spatio-temporal channel correlation. Through the analysis, we reveal that the zero-th order polynomial becomes optimal when the optimum-weighting is employed. Furthermore, we propose an efficient recursive algorithm for channel tracking in oder to reduce the computational complexity. Since the proposed scheme automatically adapts the weighting coefficients to the channel condition, it has a significant advantage in mean-square error (MSE) performance compared to EW-RLS scheme.; Engineering and Applied Sciences

Channel estimation and optimal resource allocation of relay assisted communication systems

Jia, Yupeng ; Vosoughi, Azadeh
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:ix, 147 leaves; Illustrations:ill. (some col.)
Português
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67.716157%
Thesis (Ph. D.)--University of Rochester. Dept. of Electrical and Computer Engineering, 2012.; Exploding demand for various wireless services has fueled significant development of wireless communication systems and networks in the past few decades. Wireless service providers are continuously striving to improve the design of communication systems and to enable higher data rate and more reliable wireless transmission. A major challenge in designing these systems is the random nature of the wireless transmission media due to the fading process. A recent paradigm shift from the conventional point-to- point communications is relay assisted communications. Motivated by the great success of multiple-input multiple-output (MIMO) wireless communication systems, with multiple transmit and receive antennas, researchers have considered relay assisted communications. Relying on the broadcast nature of the wireless media, a relay assisted communication system emulates a virtual MIMO system and exploits the spatial diversity, also known as cooperative diversity. Cooperative diversity increases the transmission reliability and coverage, without expanding the expenditure of the scarce transmission resources (power and bandwidth). Recently...

Secure on-off transmission design with channel estimation errors

Zhou, Xiangyun; He, Biao
Fonte: IEEE Xplore Publicador: IEEE Xplore
Tipo: Artigo de Revista Científica Formato: 14 pages
Português
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Physical layer security has recently been regarded as an emerging technique to complement and improve the communication security in future wireless networks. The current research and development in physical layer security are often based on the ideal assumption of perfect channel knowledge or the capability of variable-rate transmissions. In this paper, we study the secure transmission design in more practical scenarios by considering channel estimation errors at the receiver and investigating both fixed-rate and variable-rate transmissions. Assuming quasi-static fading channels, we design secure on-off transmission schemes to maximize the throughput subject to a constraint on secrecy outage probability. For systems with given and fixed encoding rates, we show how the optimal on-off transmission thresholds and the achievable throughput vary with the amount of knowledge on the eavesdropper’s channel. In particular, our design covers the interesting case where the eavesdropper also uses the pilots sent from the transmitter to obtain imperfect channel estimation. An interesting observation is that using too much pilot power can harm the throughput of secure transmission if both the legitimate receiver and the eavesdropper have channel estimation errors...

Multiuser Channel Estimation and Tracking for Long Code CDMA Systems

Bhashyam, Srikrishna; Aazhang, Behnaam; Bhashyam, Srikrishna; Aazhang, Behnaam
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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Journal Paper; Channel estimation techniques for code-division multiple access (CDMA) systems need to combat multiple access interference (MAI) effectively. Most existing estimation techniques are designed for CDMA systems with short repetitive spreading codes. However, current and next generation wireless systems use long spreading codes whose period is much larger than the symbol duration. In this paper, we derive the maximum likelihood channel estimate for long code CDMA systems over multipath channels using training sequences and approximate it using an iterative alogrithm to reduce the computational complexity in each symbol duration. The iterative channel estimate is also shown to be asymptotically unbiased. The effectiveness of the iterative channel estimator is demonstrated in terms of squared error in estimation as well as the bit error rate performance of a multistage detector based on the channel estimates. The effect of error in decision feedback from the multistage detector (used in the absence of training sequences) is also shown to be neglible for reasonable feedback error rates using simulations. The proposed iterative channel estimation technique is also extended to track slowly varying multipath fading channels using decision feedback. Thus...

Multiuser Channel Estimation for Long Code CDMA Systems

Bhashyam, Srikrishna; Aazhang, Behnaam; Bhashyam, Srikrishna; Aazhang, Behnaam
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Conference paper
Português
Relevância na Pesquisa
67.667554%
Conference Paper; Channel estimation techniques for code-division multiple access (CDMA) systems need to combat multiple access interference (MAI) effectively. Most existing estimation techniques are designed for CDMA systems with short repetitive spreading codes. However, current and next generation wireless systems use long spreading codes whose period is much larger than the symbol duration. In this paper, we derive the maximum likelihood channel estimate for long code CDMA systems over multipath channels using training sequences and approximate it using an iterative algorithm to reduce the computational complexity in each processing window. The asymptotic convergence of the mean of the iterative estimate to the actual channel is also shown. The effectiveness of the iterative channel estimator is demonstrated in terms of squared error in estimation as well as the bit error rate performance of a multistage detector based on the channel estimates. Finally, the proposed iterative channel estimation technique is extended to track slowly varying multipath fading channels using decision feedback. Thus, an MAI resistant multiuser channel estimate with reasonable computational complexity is derived for long code CDMA systems over multipath fading channels.

Transceiver Design for Efficient Channel Estimation in MIMO OFDM Systems

Lou, Feifei; Lou, Feifei
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
67.648447%
Masters Thesis; In this thesis, we first compare the least squares (LS) channel estimation performance in terms of mean squared error (MSE) with the perfect knowledge of channel length $L$ versus the estimation without the knowledge of $L$. This comparison motivates us to estimate the channel in two steps by exploiting the instantaneous delay spread. We show that the channel estimation performance can be improved by $5$ dB even in the presence of channel mismatch. Then we propose the optimal training sequence which achieves not only the minimum MSE of LS channel estimation, but also the minimum peak-to-average power ratio (PAPR) at transmitter with a low computational complexity. Finally we describe all the necessary synchronization functions and FPGA implementation in the SISO OFDM receiver. And this receiver serves as the foundation to build up a wireless testbed to verify the new algorithms.

Joint Multiuser Channel Estimation and Detection for CDMA Systems

Sengupta, Chaitali; Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam; Sengupta, Chaitali; Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Conference paper
Português
Relevância na Pesquisa
67.624683%
Conference Paper; We focus on the design of multiuser receiver structures for Code Division Multiple Access (CDMA) communication systems, in the presence of multipath effects and multiple sensors at the base station receiver. The joint channel estimation and detection approach presented in this paper uses a miximum likelihood approach to estimate an effective spreading code [1] vector of each user. We design our channel estimation algorithm to estimate this vector in a computationally efficient manner, instead of focusing on estimation of the individual channel parameters, such as path delays, attenuation factors, and direction of arrival. We present a framework that allows the use of the estimated effective spreading code in the detection process [2] and facilitates the development of a computationally efficient solution to the combined problem of channel estimation and multi-shot detection in a scenario involving multiple users, multiple paths, and multiple sensors.

On Multipath Channel Estimation for CDMA Systems Using Multiple Sensors

Sengupta, Chaitali; Cavallaro, Joseph R.; Aazhang, Behnaam; Sengupta, Chaitali; Cavallaro, Joseph R.; Aazhang, Behnaam
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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Journal Paper; This paper focuses on the design of a multiuser receiver structure for the reverse link of a code-division multiple-access communication system, in the presence of multipath effects and using an antenna array at the base station receiver. The algorithm presented in this paper solves the complex multidimensional problem of channel estimation in this complex scenario using a maximum-likelihood approach. This channel estimation technique requires the transmission of a training sequence or feedback of detected data. Once a composite channel-impulse response of each user is estimated, it is directly used in the detection process instead of first extracting the individual channel parameters, such as path delays and attenuation factors. The paper presents a framework that facilitates a computationally efficient solution to the combined problem of channel estimation and detection in a scenario involving multiple users, multiple paths, and multiple sensors at the receiver.

Algorithms and Architectures for Channel Estimation in Wireless CDMA Communication Systems

Sengupta, Chaitali; Sengupta, Chaitali
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text; Text
Português
Relevância na Pesquisa
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PhD Thesis; Wireless cellular communication is witnessing a rapid growth in markets, technology, and range of services. An attractive approach for economical, spectrally efficient, and high quality digital cellular and personal communication services is the use of code division multiple access (CDMA) technology. The estimation of channel delays along with channel attenuation and phases of different users constitutes the first stage in the detection process at the receiving base station in a CDMA communication system. This stage, called channel parameter estimation, forms the bottleneck for the detection of users' bitstreams; both in terms of accuracy as well as execution time. In this thesis, we develop new algorithms and architectures to solve the CDMA channel estimation problem. We have first developed a framework that facilitates a computationally efficient solution to the combined problem of channel estimation and detection in a scenario involving multiple users, multiple paths, and multiple sensors at the receiver. The channel estimation approaches presented in this thesis, consist of two categories: (1) maximum likelihood based schemes, and (2) signal and noise subspace based schemes. The maximum likelihood approach is used to solve the complex multidimensional problem of channel estimation in the presence of multipath effects and concurrently using an antenna array at the base station receiver. Once the composite channel impulse response of each user is estimated...

Blind Algorithms for Channel Estimation and Detection in Wireless Handsets

Livingston, Frank; Cavallaro, Joseph R.; Livingston, Frank; Cavallaro, Joseph R.
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Report; Text; Text
Português
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Report; Multiple access is an important consideration in the design and implementation of wireless communications systems. Code division multiple access (CDMA) is one method for providing multiple access in a wireless system. In CDMA, each user is assigned a unique code that identifies the user to the system. This code is used to modulate and demodulate the user's data. CDMA has several advantages over other more traditional multiple access methods like frequency-division multiple access (FDMA) and time-division multiple access (TDMA), one of the most important being its inherent noise-rejection capability. Because of its advantages over other multiple access methods, CDMA is being designed into many current and next-generation wireless systems. Two important functions in a wireless system are channel estimation and detection. Signals transmitted through a wireless channel are attenuated and delayed by the channel, and the purpose of channel estimation is to estimate this attenuation and delay. The purpose of detection is to detect the information symbols contained in the received signal. For reasons of size, power, and cost, the handsets in a wireless system have fewer resources than the base stations in the system and less knowledge than the base stations concerning the other users in the system. Because of this...

Implementation of Channel Estimation and Multiuser Detection Algorithms for W-CDMA on Digital Signal Processors

Rajagopal, Sridhar; Xu, Gang; Cavallaro, Joseph R.; Rajagopal, Sridhar; Xu, Gang; Cavallaro, Joseph R.
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Conference paper; Text; Text
Português
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Conference Paper; Proposed algorithms for Third Generation W-CDMA communication systems have extremely high performance requirements. In this paper, we study the implementation issues involved for one of the proposed multiuser channel estimation and detection algorithms for base-stations in the uplink using TI's TMS320C6x DSP Evaluation Modules(EVM). It was found that these proposed algorithms for multiuser channel estimation and detection have different processing and precision requirements. While the detector can be implemented using the C6201 16-bit fixed point DSP, the proposed channel estimation algorithm may be more suitable for a oating point implementation using the C6701 floating point DSP. We study the effects of the specialized approximate instructions available on the C6701 DSP on channel estimation. Then, the advantage of multistep optimizations and use of assembly code is studied for both the algorithms. Memory issues involved in the implementation of these algorithms is also investigated. It was found that the data memory requirements for channel estimation for the chosen system parameters necessitates the use of external memory while the multistage detection algorithm could be placed in the available internal data memory. We finally discuss the current and future trends of DSPs and their utilization for such wireless communication applications.; Nokia

Two-way discriminatory channel estimation for non-reciprocal wireless MIMO channels

Huang, Chao-Wei; Chang, Tsung-Hui; Zhou, Xiangyun; Hong, Y.-W. Peter
Fonte: IEEE Publicador: IEEE
Tipo: Conference paper Formato: 5 pages
Português
Relevância na Pesquisa
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The idea of discriminatory channel estimation (DCE) was recently proposed to differentiate the performance at a legitimate receiver (LR) and an unauthorized receiver (UR) by carefully designing the training phase of transmission. In particular, an artificial noise (AN) signal is inserted into the training signal to degrade the channel estimation performance at UR. However, without careful design, the inserted AN may potentially leak into LR's channel causing degradation in LR's performance. In order to minimize such an undesirable AN leakage, the transmitter must acquire sufficient knowledge of the downlink channel to LR for careful signalling, which is particularly difficult to achieve in non-reciprocal channel environments. In this work, we design a DCE scheme with multiple training stages to achieve this task. The key feature of the proposed scheme is to utilize a two-way training scheme that allows both the transmitter and LR to collaboratively send different training signals to achieve DCE. Simulation results demonstrate that our proposed scheme is able to achieve accurate channel estimation and data detection performances at LR, while severely degrading UR's performances.; This work was supported by in part by the National Science Council...

Two-way training for discriminatory channel estimation in wireless MIMO systems

Huang, Chao-Wei; Chang, Tsung-Hui; Zhou, Xiangyun; Hong, Y.-W. Peter
Fonte: Institute of Electrical and Electronics Engineers (IEEE) Publicador: Institute of Electrical and Electronics Engineers (IEEE)
Tipo: Artigo de Revista Científica Formato: 15 pages
Português
Relevância na Pesquisa
67.78687%
This work examines the use of two-way training to efficiently discriminate the channel estimation performances at a legitimate receiver (LR) and an unauthorized receiver (UR) in a multiple-input multiple-output (MIMO) wireless system. This work improves upon the original discriminatory channel estimation (DCE) scheme proposed by Chang where multiple stages of feedback and retraining were used. While most studies on physical layer secrecy are under the information-theoretic framework and focus directly on the data transmission phase, studies on DCE focus on the training phase and aim to provide a practical signal processing technique to discriminate between the channel estimation performances (and, thus, the effective received signal qualities) at LR and UR. A key feature of DCE designs is the insertion of artificial noise (AN) in the training signal to degrade the channel estimation performance at UR. To do so, AN must be placed in a carefully chosen subspace, based on the transmitter's knowledge of LR's channel, in order to minimize its effect on LR. In this paper, we adopt the idea of two-way training that allows both the transmitter and LR to send training signals to facilitate channel estimation at both ends. Both reciprocal and nonreciprocal channels are considered and a two-way DCE scheme is proposed for each scenario. For mathematical tractability...

Iterative Receiver Techniques for Data-Driven Channel Estimation and Interference Mitigation in Wireless Communications

Zhao, Ming
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Thesis (PhD); Doctor of Philosophy (PhD)
Português
Relevância na Pesquisa
67.68335%
Wireless mobile communications were initially a way for people to communicate through low data rate voice call connections. As data enabled devices allow users the ability to do much more with their mobile devices, so to will the demand for more reliable and pervasive wireless data. This is being addressed by so-called 4th generation wireless systems based on orthogonal frequency division multiplexing (OFDM) and multiple-input multiple-output (MIMO) antenna systems. Mobile wireless customers are becoming more demanding and expecting to have a great user experience over high speed broadband access at any time and anywhere, both indoor and outdoor. However, these promising improvements cannot be realized without an e±cient design of the receiver. Recently, receivers utilizing iterative detection and decoding have changed the fundamental receiver design paradigm from traditional separated parameter estimation and data detection blocks to an integrated iterative parameter estimator and data detection unit. Motivated by this iterative data driven approach, we develop low complexity iterative receivers with improved sensitivity compared to the conventional receivers, this brings potential benefits for the wireless communication system, such as improving the overall system throughput...

Vectorial channel estimation for uplink MC-CDMA in beyond 3G wireless systems

Marques, P.; Gameiro, A. S.
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
67.581157%
In beyond 3G wireless systems the bandwidth efficiency can be increased with the use of adaptive antenna arrays. This paper focus on a key issue for adaptive antenna arrays, that is, channel parameters estimation including Direction-Of-Arrival (DOA). In order to estimate DOA. the channel frequency responses for the links between the mobile users and each of base station array elements are estimated by pilot-aided minimum mean square error (MMSE) algorithm. This estimator is not sensitive to the channel statistics. Based on frequency response estimatives DOA's of impinging multipath components to the base station are estimated by a low complex Wlauimuni Likelihood (ML) approach. Furthermore an uplink burst structure with specifically designed midamble field for multiuser channel estimation in MC-CDMA is proposed. The performance is assessed in terms of channel estimation errors for a MC-CDMA TDD system over fast and slow fading mobile channels.

Channel estimation method with improved performance for the UMTS-TDD mode

Marques, Paulo; Gameiro, A.; Fernandes, J.
Fonte: Springer Verlag Publicador: Springer Verlag
Tipo: Artigo de Revista Científica
Português
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67.70406%
Channel estimation is an essential building block for UTRA-TDD high performance receivers. Once the performance of the channel estimator algorithm proposed by 3GPP is highly dependent on the time spreading between consecutive multi-path components, a Successive Multi-path channel Estimation Technique (SMET) that improves the time resolution is proposed in this paper. A SMET based maximum likelihood approach for vectorial channel estimation, to include the estimation of the direction-of-arrival, is also proposed. This algorithm solves efficiently the complex problem of DOA estimation of multiple users in a multi path propagation environment even when the number of required DOA's exceeds the number of antenna array elements. Another property of the proposed algorithm is its ability to resolve signals from different users arriving from the same direction. This is due to processing in both time and space dimensions. The performance of these algorithms is assessed by resorting to simulations in multi-path environments using the UMTS-TDD specifications, and also by comparing the rms estimation errors against the Crámer-Rao Bound. The effect of imperfect channel estimation on the performance of RAKE and Hard-Decision Parallel Interference Canceller receivers is also analysed. The results show that a good performance can be achieved with SMET...

Enhanced MMSE Channel Estimation Using Timing Error Statistics for Wireless OFDM Systems

Athaudage, Chandranath R; Jayalath, Anagiyaddage Dhammik
Fonte: Institute of Electrical and Electronics Engineers (IEEE Inc) Publicador: Institute of Electrical and Electronics Engineers (IEEE Inc)
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
67.700464%
Estimation and tracking of the frequency-selective time-varying channel response is a challenging task for wireless communication systems incorporating coherent OFDM. In pilot-symbol-assisted (PSA) OFDM systems, the minimum mean-square-error (MMSE) estimator provides the optimum performance based on the channel statistics (channel correlation function and SNR). In OFDM systems, FFT-block timing error introduces a linear phase rotation to data modulated on individual subcarriers. An MMSE channel estimator designed only using the wireless channel statistics performs only sub-optimally when sub-carrier phase rotations due to block timing errors are present. In this paper, we show that by using the block timing error statistics of the OFDM time-synchronizer the performance of the MMSE channel estimation can be significantly improved. Numerical results show that the bit-error-probability (BEP) performance degradation due to timing errors can be almost completely recovered by the proposed technique.

Low-complexity channel estimation for wireless OFDM systems

Athaudage, Chandranath R; Jayalath, Anagiyaddage Dhammik
Fonte: Institute of Electrical and Electronics Engineers (IEEE Inc) Publicador: Institute of Electrical and Electronics Engineers (IEEE Inc)
Tipo: Conference paper
Português
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Wireless communication systems incorporating coherent OFDM requires the estimation and tracking of the time-varying channel response for accurate demodulation of data at the receiver. In pilot-symbol-assisted (PSA) OFDM systems, the minimum mean-square-error (MMSE) estimator is a good channel estimation technique given that channel statistics are known. However, the major drawback of the MMSE estimator is its high computational complexity, which grows with number of pilots. Piecewise-linear interpolation is a low complexity solution to the channel estimation task. In this paper we derive exact expressions for the channel estimation error as a function of pilot spacing, channel statistics and channel noise, when piecewise-linear interpolation is incorporated. We compare the performance of piecewise-linear interpolation against that of a low complexity MMSE technique (piecewise-MMSE interpolation) under both matched and mismatched conditions of channel statistics. Results show that a piecewise-linear interpolator performs better than a mismatched piecewise-MSSE interpolator of same complexity.