Philippa A. Martin

University of Canterbury, Christchurch, Canterbury, New Zealand

Are you Philippa A. Martin?

Claim your profile

Publications (41)43.05 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this study, the authors design a multi-user ultra-wideband system for indoor wireless communication. The proposed system is useful in multipath radio reception as the full multipath diversity gain is achieved. The system has multiple transmitters and receivers. They use polyphase spreading waveforms which feature low levels of mutual interference and enable each of the channel impulse responses to be measured free from distortion continuously with each data symbol transmission. A key feature of the proposed system is that transmitted waveforms are used which produce outputs from the receiver cross correlators, which are zero on both sides of the main correlation peak, for each radio path. This zero response lasts for a duration in excess of the expected delay spread of the radio channel enabling full Rake processing of the multipath signal. The effects of the low levels of mutual interference are reduced further by using time and frequency hopping, forward error correction and soft decision decoding.
    No preview · Article · Mar 2015 · IET Communications
  • Uzma Afsheen · Peter J. Smith · Philippa A. Martin
    [Show abstract] [Hide abstract]
    ABSTRACT: It is known that the performance of limited feedback precoding systems depends on the size of the codebook, determined by the number of feedback bits. Increasing the number of feedback bits improves performance. However, this in turn requires a significant increase in the control channel bandwidth. The goal of the proposed reconfigurable antenna codebook scheme is to improve the closed-loop precoding gain without increasing the number of feedback bits. We employ reconfigurable antennas at the receiver resulting in multiple possible channel conditions. We have shown through simulations that increasing the number of receive antenna states has the same effect as a bigger codebook in terms of received signal to noise ratio gain, improved symbol error rate and sum rate gain. Different codeword and RA state selection methods are considered for both single and multi-layer transmissions and different system sizes, using LTE and Grassmannian codebooks with MMSE and SVD receivers.
    No preview · Conference Paper · Feb 2014
  • Source
    Dushyantha A. Basnayaka · Peter J. Smith · Philippa A. Martin
    [Show abstract] [Hide abstract]
    ABSTRACT: The prospect of base station cooperation leading to joint combining at widely separated antennas has led to increased interest in macrodiversity systems, where both sources and receive antennas are geographically distributed. In this scenario, analytical investigation of channel capacity is extremely challenging for finite-size systems since the channel matrices have a very general form where each path may have a different power. Hence, in this paper, we consider the ergodic sum capacity of a macrodiversity multiple-input multiple-output system with arbitrary numbers of sources and receive antennas operating over Rayleigh fading channels. For this system, we compute the exact ergodic capacity for a system with at most two transmit antennas and a compact approximation for the general system, which is shown to be very accurate over a wide range of cases. Finally, we compare our results with previous asymptotic results and bounds. Results are verified by Monte Carlo simulations and the impact on capacity of various channel power profiles is investigated.
    Preview · Article · Sep 2013 · IEEE Transactions on Information Theory
  • Uzma Afsheen · Philippa A. Martin · Peter J. Smith
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we propose a novel class of space time trellis codes based on super quasi-orthogonal space time codes for a reconfigurable antenna system. We call them Space Time State Trellis Codes (STSTCs). The proposed codes are capable of taking advantage of the additional degrees of diversity offered by reconfigurable antennas and changing propagation states. They achieve full rate, full diversity and high coding gain. Simulation results demonstrate their good performance. STSTCs achieve the diversity order expected for four transmit antennas while using only two reconfigurable transmit antennas. Our code out performs the existing super orthogonal space time trellis code, which fails to achieve full diversity in a reconfigurable antenna system.
    No preview · Conference Paper · Sep 2013
  • Tri Pham · Philippa A. Martin · Desmond P. Taylor · Clive Horn
    [Show abstract] [Hide abstract]
    ABSTRACT: We consider single-h continuous phase modulation (CPM) systems that use linear prediction receivers with coefficient look up table (LUT) for mitigating the effect of multipath fading. This type of receiver shows superior performance over conventional ones; however, high channel delay spread and fast fading can still lead to a high error floor in its performance. A sub-optimal soft/iterative detection based on the soft output Viterbi algorithm (SOVA) is presented for reducing such error floors while maintaining low complexity. The design is extended with a simple spatial diversity combining scheme and the utilization of multiple coefficient LUTs. The proposed approach allows a significant performance gain to be achieved.
    No preview · Conference Paper · Jun 2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: This book introduces the theoretical elements at the basis of various classes of algorithms commonly employed in the physical layer (and, in part, in MAC layer) of wireless communications systems. It focuses on single user systems, so ignoring multiple access techniques. Moreover, emphasis is put on single–input single–output (SISO) systems, although some relevant topics about multiple–input multiple–output (MIMO) systems are also illustrated. Comprehensive wireless specific guide to algorithmic techniques Provides a detailed analysis of channel equalization and channel coding for wireless applications Unique conceptual approach focusing in single user systems Covers algebraic decoding, modulation techniques, channel coding and channel equalisation
    No preview · Book · May 2013
  • Dushyantha A. Basnayaka · Peter J. Smith · Philippa A. Martin
    [Show abstract] [Hide abstract]
    ABSTRACT: The performance of maximal ratio combining (MRC) in Rayleigh channels with co-channel interference (CCI) is well-known for receive arrays which are co-located. Recent work in network MIMO, edge-excited cells and base station collaboration is increasing interest in macrodiversity systems. Hence, in this paper we consider the effect of macrodiversity on MRC performance in Rayleigh fading channels with CCI. We consider the uncoded symbol error rate (SER) as our performance measure of interest and investigate how different macrodiversity power profiles affect SER performance. This is the first analytical work in this area. We derive approximate and exact symbol error rate results for M-QAM/BPSK modulations and use the analysis to provide a simple power metric. Numerical results, verified by simulations, are used in conjunction with the analysis to gain insight into the effects of the link powers on performance.
    No preview · Article · Apr 2013 · IEEE Transactions on Communications
  • Source
    Dushyantha A. Basnayaka · Peter J. Smith · Philippa A. Martin
    [Show abstract] [Hide abstract]
    ABSTRACT: The performance of linear receivers in the presence of co-channel interference in Rayleigh channels is a fundamental problem in wireless communications. Performance evaluation for these systems is well-known for receive arrays where the antennas are close enough to experience equal average SNRs from a source. In contrast, almost no analytical results are available for macrodiversity systems where both the sources and receive antennas are widely separated. Here, receive antennas experience unequal average SNRs from a source and a single receive antenna receives a different average SNR from each source. Although this is an extremely difficult problem, progress is possible for the two-user scenario. In this paper, we derive closed form results for the probability density function (pdf) and cumulative distribution function (cdf) of the output signal to interference plus noise ratio (SINR) and signal to noise ratio (SNR) of minimum mean squared error (MMSE) and zero forcing (ZF) receivers in independent Rayleigh channels with arbitrary numbers of receive antennas. The results are verified by Monte Carlo simulations and approximations and high SNR analysis are also derived. The results enable further system analysis such as the evaluation of outage probability, bit error rate (BER) and capacity.
    Preview · Article · Dec 2012 · IEEE Transactions on Wireless Communications
  • Dushyantha A. Basnayaka · Peter J. Smith · Philippa A. Martin
    [Show abstract] [Hide abstract]
    ABSTRACT: In this letter, we consider the effect of macrodiversity on the performance of maximum likelihood detection in flat Rayleigh/Rician fading. Macrodiversity MIMO, where both the transmit antennas and receive antennas are widely separated, is becoming increasingly important with the advent of network MIMO, edge excited cells, base station cooperation, etc. The analysis builds on an exact evaluation of the pairwise error probability which leads to a union bound for symbol error rate (SER). SER results are shown, as well as a diversity analysis and an investigation of the impact of macrodiversity.
    No preview · Article · Nov 2012 · IEEE Communications Letters
  • Zahid Rauf · Philippa A. Martin · Desmond P. Taylor
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose two schemes to perform multiuser detection (MUD) for multiuser multiple-input multiple-output (MIMO) systems under overload. Typically linear MUD algorithms fail to perform under overload and maximum likelihood detection is often prohibitively complex. In this paper, we use hybrid automatic repeat request (HARQ) retransmissions to transform an overloaded system into a critically or underloaded system based on the concept of virtual receive antennas. Hence, low complexity linear MUD algorithms can be used and achieve diversity gains. Simulation results clearly highlight the advantages obtained by the proposed schemes.
    No preview · Conference Paper · Nov 2012
  • Khawaja Tauseef Tasneem · Philippa A. Martin · Desmond P. Taylor
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose an iterative soft multiuser detection technique for detecting multiple BPSK modulated cochannel signals in Rayleigh flat fading environments. Ant colony optimization is used to produce soft estimates of the transmitted signals. Our attention is focused on the challenging case of overloaded transmission, where there are fewer receive antennas than transmitted cochannel signals. Simulation results show our approach can achieve near maximum likelihood (ML) performance at significantly reduced complexity for critically loaded systems, and it continues to provide good performance under overloaded scenarios.
    No preview · Conference Paper · Sep 2012
  • Source
    Dushyantha A. Basnayaka · Peter J. Smith · Philippa A. Martin
    [Show abstract] [Hide abstract]
    ABSTRACT: The performance of maximal ratio combining (MRC) in Rayleigh channels with co-channel interference (CCI) is well-known for receive arrays which are co-located. Recent work in network MIMO, edge-excited cells and base station collaboration is increasing interest in macrodiversity systems. Hence, in this paper we consider the effect of macrodiversity on MRC performance in Rayleigh fading channels with CCI. We consider the uncoded symbol error rate (SER) as our performance measure of interest and investigate how different macrodiversity power profiles affect SER performance. This is the first analytical work in this area. We derive approximate and exact symbol error rate results for M-QAM/BPSK modulations and use the analysis to provide a simple power metric. Numerical results, verified by simulations, are used in conjunction with the analysis to gain insight into the effects of the link powers on performance.
    Preview · Article · Aug 2012
  • Rui Lin · Philippa A. Martin · Desmond P. Taylor
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, the non-selective Decode-and-Forward (DF) scheme proposed in is analyzed using approximate Gaussian density evolution (DE). Based on the DE analysis, performance is shown to be improved by adaptively changing the transmit code at the relay node in response to the channel conditions. Simulation results show that the proposed adaptive scheme improves performance, particularly when the relay is closer to the destination than to the source. In addition, the adaptive scheme does not increase network overhead.
    No preview · Article · Aug 2012 · IEEE Transactions on Communications
  • Peter J. Smith · Abdulla Firag · Philippa A. Martin · Ross Murch
    [Show abstract] [Hide abstract]
    ABSTRACT: Reconfigurable antenna arrays offer advantages over traditional antenna selection in terms of requiring fewer physical antennas and the use of fixed antenna feeds. Hence, in this paper we analyze the signal to noise ratio (SNR) improvement offered by reconfigurable antennas and compare it to traditional selection. Both the distribution and the mean value of the link gains in a reconfigurable system are derived and used to gain insight into system performance, both for SNR gain and outage. Results demonstrate that for systems with up to four antennas and two radiation states, reconfiguration can provide at least 76% of the improvements offered by selection.
    No preview · Article · Apr 2012 · IEEE Communications Letters
  • Source
    Philippa A. Martin · Peter J. Smith · Ross Murch
    [Show abstract] [Hide abstract]
    ABSTRACT: Space-time block codes typically only span a small number of time slots. However, error control coding spanning hundreds or thousands of symbol periods is often used with space-time coding. In this case, slow fading channels significantly degrade performance. In this letter, we show that performance can be significantly improved in slow fading conditions by using reconfigurable antennas. We propose switching the transmit antenna states during transmission so that the error control code experiences several different channel conditions over the transmission period. Hence, it can achieve higher diversity and the superior performance expected of a faster fading channel due to reconfigurable antenna state switching. If we also allow the receiver to select the reconfigurable receive antenna states based on channel energy, then an antenna state selection gain is also achieved.
    Full-text · Article · Apr 2012 · IEEE Communications Letters
  • Michael Krause · Desmond P. Taylor · Philippa A. Martin
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the use of the minimum mean-squared- error decision-feedback-equalizer (MMSE-DFE) as a preprocessor to reduce the computational complexity of symbol detection in frequency-selective multiple- input multiple-output (MIMO) channels. The preprocessor delays and focuses the received signal energy which reduces the effects of inter-symbol- interference and multiple-access-interference. This property of the MMSE-DFE preprocessor is exploited to order and to reduce the number of symbol candidates considered by an iterative maximum- likelihood (ML) detector. Simulations show that the proposed detection scheme can achieve lower bit- error-rates than existing reduced-complexity algorithms in overdetermined and underdetermined receive scenarios. Near-optimum performance is achieved when the number of symbol candidates is increased.
    No preview · Conference Paper · Dec 2011
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: With the ever increasing interest in multiple-input multiple-output (MIMO) cognitive radio (CR) systems, reducing the costs associated with RF-chains at the radio front end becomes a very important factor. In this paper, we propose two solutions to the problem of joint transmit-receive antenna selection with the objective of maximizing data rates and satisfying interference constraints at the primary user (PU) receiver. In the first method we approximate the original non-convex optimization problem with an iterative way of solving a series of smaller convex problems. Then we present a novel, norm-based transmit receive antenna selection technique that simultaneously improves throughput while maintaining the PU interference constraints. We show that this simple approach yields near optimal results with massive complexity reductions. In addition to making a performance comparison between the proposed approaches and the optimal exhaustive search approach, we establish that antenna selection is a promising option for future MIMO CR devices.
    Preview · Article · Nov 2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we propose two solutions to the problem of joint transmit-receive antenna selection in a multiple-input multiple-output (MIMO) cognitive radio (CR) system. Our objective is to maximize CR data rates and satisfy interference constraints at the primary user (PU) receiver(s). In the first we approximate the original non-convex optimization problem using an iterative approach solving a series of smaller convex problems. Second we present a novel, norm-based transmit receive antenna selection technique that simultaneously improves throughput while maintaining the PU interference constraints. We show that this approach yields near optimal results with massive complexity reductions. We make a performance comparison between the proposed approaches and the optimal exhaustive search approach. We provide an analysis of the exhaustive search and relate selection gains to system parameters such as the shadow fading standard deviation, the path loss exponent and the number of PUs per square kilometer. Our results establish that antenna selection is a promising option for future MIMO CR devices in sparse PU environments.
    No preview · Article · Nov 2011 · IEEE Transactions on Wireless Communications
  • Gayathri Kongara · Desmond P. Taylor · Philippa A. Martin
    [Show abstract] [Hide abstract]
    ABSTRACT: We consider the detection of multiple cochannel single-carrier spatially multiplexed data streams. To this end, we propose a hybrid time-frequency-domain decision feedback equalizer, which performs parallel detection of the data streams. A practical parameter estimation algorithm for these receivers is developed, which estimates the MIMO channel in parallel as a set of effective channel vectors. To avoid interference cancellation, we develop a two-stage frequency-domain (FD) forward section that implements linear cochannel interference (CCI) suppression in cascade with equalization utilizing estimated channel-state information. The resulting receiver architecture outperforms interference-cancellation-based equalizers in the presence of channel estimation errors. Furthermore, all transmitted data streams achieve equal diversity gains.
    No preview · Article · Jun 2011 · IEEE Transactions on Vehicular Technology
  • Michael Krause · Desmond P. Taylor · Philippa A. Martin
    [Show abstract] [Hide abstract]
    ABSTRACT: Co-channel interference (CCI) occurs in a wireless receiver when multiple signals are present. The receiver experiences excessive CCI under overload which occurs when there are more signals than receive antennas. This makes separation and estimation of the transmitted data signals difficult. We develop a novel reduced-complexity receiver structure for the separation and symbol detection of multiple co-channel signals in frequency-flat Rayleigh fading channels. Moreover, we show that list-based group-wise processing can achieve better performance at low and moderate signal-to-noise ratios than existing group-wise soft information processing schemes. The receiver is equipped with multiple antennas and developed to work under overload. Its structure consists of a linear preprocessor followed by a nonlinear reduced-complexity symbol detector. The proposed list group-search detection (LGSD) algorithm relies on list feedback and reduces complexity by iteratively searching over groups of transmitted symbols. It outputs a list of likely data symbols which is well suited to further processing using soft input error control decoders. Simulation shows that LGSD can achieve near optimum joint maximum likelihood performance under overload at significantly lower complexity.
    No preview · Article · May 2011 · IEEE Transactions on Wireless Communications