IET Communications
Print ISSN
1751-8628
Online ISSN 1751-8636
Online ISSN 1751-8636
IET Communications covers the fundamental and generic research for a better understanding of communication technologies to harness the signals for better performing communication systems using various wired and/or wireless media. This Journal is particularly interested in research papers reporting novel solutions to the dominating problems of noise, interference, timing and errors for reduction systems deficiencies such as wasting scarce resources such as spectra, energy and bandwidth.
This publication was previously known as IEE Proceedings - Communications 1994-2006. ISSN 1350-2425. more..
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Distributed space-time trellis codes with continuous phase modulation for amplify and forward relaying
- Author(s): Ali Serdar Demiroğlu; Íbrahim Altunbaş
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p.
110
–118
(9)
Continuous phase modulation (CPM) is a non-linear power/bandwidth efficient modulation method. Linear modulation methods such as phase shift keying or quadrature amplitude modulation produce large power drain at the power amplifier of the transmitter. Therefore CPM may be an alternative to these modulations in relay/cooperative systems because of its constant envelope property, which enables us to use inexpensive and energy-efficient non-linear power amplifiers. In this study, the authors investigate optimum distributed space-time CPM trellis codes for amplify and forward relaying systems with one to four relays and specifically consider minimum shift keying and quaternary continuous phase frequency shift keying with modulation indices of 1/2 and 1/4. Novel distributed space-time CPM trellis codes are obtained. Error performances of the novel codes and their classical counterparts are compared over frequency non-selective quasi-static Rayleigh-fading channels using the Viterbi algorithm at the destination terminal and superiority of the novel codes are presented.
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Efficient cooperative spectrum sensing for three-hop cognitive wireless relay networks
- Author(s): Quoc-Tuan Vien; Brian G. Stewart; Huaglory Tianfield; Huan X. Nguyen
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p.
119
–127
(9)
This study is concerned with cooperative spectrum sensing (CSS) mechanisms in three-hop cognitive wireless relay networks (CWRNs). The data transmission from a source to a destination is realised with the aid of two layers of cognitive radio (CR) users which are in the transmission coverage of two primary users. The authors first propose a new CSS scheme for a layer of CR users to improve the spectrum-sensing performance by exploiting both local decisions at the CR users and global decisions at the fusion centre. Particularly, the probabilities of missed detection and false alarm for a practical scenario where all sensing, reporting and backward channels suffer from Rayleigh fading are derived. The derived expressions not only show that the proposed CSS achieves a better sensing performance than the conventional scheme but also characterise the effects of the fading channels on the sensing reliability. Furthermore, the authors propose a CSS scheme for two CR layers in a three-hop CWRN using binary operations to help reduce one phase of sensing for a higher system throughput.
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Optimisation of power allocation for asymmetric relay placement in multi-hop relay systems
- Author(s): Kalpana Dhaka; Ranjan K. Mallik; Robert Schober
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p.
128
–136
(9)
In this study, schemes for optimisation of power allocation (OPA) for asymmetric relay placement are presented for multi-hop communication in a Rayleigh-fading environment. For a decode-and-forward (DF) multi-hop communication system, expressions are derived for optimised power allocation based on symbol error probability (SEP) and global channel state information (GCSI). The analysis for OPA based on GCSI is extended to a hybrid combination of amplify-and-forward (AF) and DF relays. Analysis is done for two kinds of modulation schemes: M-ary phase-shift keying with coherent detection and orthogonal M-ary frequency-shift keying with non-coherent detection. Simulation results show that for a multi-hop system with asymmetric relay placement, power optimisation schemes perform better than the conventional equal power allocation scheme. In addition, power optimisation based on GCSI shows substantially improved performance compared with power allocation based on end-to-end SEP. Further, performance comparison is shown for increase in number of relay nodes in an AF and DF multi-hop system with and without power allocation. The performance of a DF system improves with increase in number of relay nodes whereas performance of an AF system degrades. Hybrid relaying provides an option to exercise switching between DF and AF so as to extract the maximum advantage of the two relaying schemes.
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Space–time coding scheme for time–frequency asynchronous two-way relay networks
- Author(s): Weile Zhang; Qinye Yin
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p.
137
–145
(9)
In this study, the authors develop a distributed space–time coding scheme for a two-way relay network that contains multiple distributed relay nodes. Both the time and frequency asynchronous nature of the distributed system are considered in the design. Distributed convolutional coding is employed to handle multiple timing errors in the networks. The authors prove that under perfect frequency synchronisation, the proposed scheme can achieve both spatial and multipath diversity by linear receivers, such as linear zero-forcing or minimum mean-square-error receiver, thus providing a low decoding complexity. The authors further find that frequency asynchronism has little effect on the designed scheme and show that the diversity can still be achieved almost surely (in the measured theoretic sense) under both time and frequency asynchronous scenarios. The authors also provide numerical results to corroborate the proposed studies.
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Average spectral efficiency of multi-modulation cellular systems
- Author(s): José Acuña; Iñigo Cuiñas
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p.
146
–151
(6)
Fourth generation systems are proposed to create extended wireless networks by applying frequency reuse techniques based on a cellular scheme. However, the total bandwidth needed depends on the channel bandwidth and the signal-to-interference protection ratio. The procedure to compute the performance of such interference-limited cellular systems is introduced in this study for systems with various modulation schemes (quadrature phase shift keying, 16 and 64 quadrature amplitude modulation), founding the percentage of the cell area that could be managed with each modulation, considering full load sectors. The conditions to share the same subcarriers between two users in next to base stations are also presented. The total bandwidth required to deploy a network with three sectored cells with 10 MHz channel results to be 360 MHz. This is a big issue since the size of the bands is generally 200 MHz, and it could limit the expected performance of these systems.
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Optimal incremental relaying in cooperative diversity systems
- Author(s): Ali H. Bastami; Ali Olfat
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p.
152
–168
(17)
One of the main drawbacks of cooperative communication systems with half-duplex relaying is inefficient use of spectrum. Incremental relaying is an effective technique that overcomes this limitation. In this study, for a single-relay regenerative system, the authors propose a spectrally-efficient incremental relaying scheme that eliminates redundant relay transmissions such that the error propagation from the relay to the destination is effectively mitigated and the full diversity is achieved. The authors examine the impact of the error propagation on the performance of the system and derive closed-form expressions for the end-to-end symbol error probability (SEP) for different modulation schemes. They also derive an approximate closed-form expression for the optimal threshold that minimises the end-to-end SEP. The high-signal-to-noise ratio (SNR) analysis demonstrates that this threshold achieves full diversity whereas neither the bandwidth-consuming cyclic redundancy check code nor the availability of the instantaneous source–relay channel state information at the destination is required in the system. Furthermore, the authors purpose a class of thresholds that are independent of the network geometry and achieve full diversity. The asymptotic behaviour of the system shows that the spectral efficiency for both the optimal and geometry-independent thresholds in the high-SNR regime tends to the maximum achievable value.
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Pulse waveforms for 60 GHz M-ary pulse position modulation communication systems
- Author(s): Hao Zhang; Ting-ting Lu; T.Aaron Gulliver
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p.
169
–179
(11)
Pulse waveforms for 60 GHz impulse radio (IR) communication systems are investigated. The power spectral densities of the pulses are examined for compliance with Federal Communications Commission (FCC) spectral regulations. The error probability and capacity of M-ary pulse position modulation (PPM) 60 GHz IR systems with a correlation receiver using different pulse waveforms are analysed. Both orthogonal and non-orthogonal PPM is considered with additive white Gaussian noise and IEEE 802.15.3c channel models. Analytical and simulation results are presented, which show that an autocorrelation function that decays quickly provides a lower probability of error and better capacity. Among the pulse waveforms examined in this study, the truncated sinc pulse is the best in terms of compliance with FCC regulations and the PPM error probability and capacity.
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Space-time coding with receive combiner bank for multiple-input–multiple-output system under multi-user cochannel interference
- Author(s): Jui Teng Wang
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p.
180
–186
(7)
Space-time coding with receive combiner bank (STC-RCB), in which a bank of receive combiners is added before the space-time decoder for interference-plus-noise suppression, is proposed. Without loss of generality, the author consider space-time block code (STBC) to be the representative of STC and study the performance for (STBC-RCB). The author derive the output signal to interference-plus-noise ratio (SINR) (of the space-time decoder) for STBC-RCB under multi-user cochannel interference. By regarding STBC as a special case of STBC-RCB, the author also derive the output SINR for STBC under multi-user cochannel interference. Simulation results show that the output SINR of STBC-RCB can be much larger than that of STBC, also, they show that STBC-RCB can adopt the appropriate receive combining strategy in the RCB to further improve the performance.
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DC-free codes with complex-valued signalling constellations
- Author(s): Craig Jamieson; Ivan Fair
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p.
91
–97
(7)
The use of spectral shaping constrained codes is commonplace in baseband digital communication systems. In this study, the authors consider the use of constrained codes in bandpass systems through the design of DC-free codes for the complex baseband representations of commonly used signalling constellations including quaternary phase shift keying, eight-phase shift keying and sixteen quadrature amplitude modulation. The authors construct DC-free codes for these signalling alphabets and present their spectral performance. They show that, similar to DC-free codes for baseband systems, the variance of the running digital sum remains a good indicator of spectral performance and that Justesen's relationship between the sum variance and cut-off frequency holds.
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Ergodic and outage capacities of relaying channels in spectrum-sharing constrained systems
- Author(s): Kaïs Ben Fredj; Sonia Aïssa; Leila Musavian
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p.
98
–109
(12)
This study investigates the capacity of multiple relay channels in different fading and shadowing environments under spectrum-sharing constraints. The authors consider that a secondary user (SU) is allowed to share the spectrum band with a primary user (PU) provided that the SU's transmit power remains below an interference power threshold set by the PU. Considering a scenario where the SU's transmitter and receiver cannot communicate directly, a relay node, chosen among a set of K terminals, helps transmitting data from the SU's transmitter to the destination. The SU's transmitter and chosen relay node adapt their corresponding transmission parameters so as to satisfy the interference-power constraint at the PU's receiver. The authors derive closed-form expressions for the ergodic capacity of the SU's channel in Rayleigh fading, Nakagami-m fading and lognormal shadowing environments. They further obtain the outage capacity assuming the aforementioned environments and the above-mentioned spectrum-sharing limitations. Numerical results are provided to reinforce our theoretical derivations.
