Always-on sound classification is a desirable but power-intensive function for a variety of emerging Internet of Everything applications. This work explores the accuracy-complexity tradeoff by using summary statistics for classifying semi-stationary sounds. Compared to contemporary solutions including deep learning, this approach requires one to three orders of magnitude fewer parameters and can therefore be trained over ten times faster. We propose a mixed-signal design using N-path filters for feature extraction to further improve energy efficiency without incurring a large accuracy penalty for a binary classification task (less than 2.5% area reduction under receiver operating characteristic curve).

Owing to limited resources, it is hard to guarantee minimum service levels to all users in conventional cellular systems. Although global cooperation of access points (APs) is considered promising, practical means of enhancing efficiency of cellular systems is by considering distributed or clustered jointly processed APs. The authors present a novel ‘quality of service (QoS) balancing scheme’ to maximise sum rate as well as achieve cell‐based fairness for clustered jointly processed cellular multiple access channel (referred to as CC‐CMAC). Closed‐form cell level QoS balancing function is derived. Maximisation of this function is proved as an NP hard problem. Hence, using power‐frequency granularity, a modified genetic algorithm (GA) is proposed. For inter site distance (ISD) < 500 m, results show that with no fairness considered, the upper bound of the capacity region is achievable. Applying hard fairness restraints on users transmitting in moderately dense AP system, 20% reduction in sum rate contribution increases fairness by upto 10%. The flexible QoS can be applied on a GA‐based centralised dynamic frequency planner architecture.

Low density signature orthogonal frequency division multiplexing (LDS-OFDM) is an uplink multi-carrier multiple access scheme that uses low density signatures (LDS) for spreading the symbols in the frequency domain. In this paper, we introduce an effective receiver for the LDS-OFDM scheme. We propose a framework to analyze and design this iterative receiver using extrinsic information transfer (EXIT) charts. Furthermore, a turbo multi-user detector/decoder (MUDD) is proposed for the LDS-OFDM receiver. We show how the turbo MUDD is tuned using EXIT charts analysis. By tuning the turbo-style processing, the turbo MUDD can approach the performance of optimum MUDD with a smaller number of inner iterations. Using the suggested design guidelines in this paper, we show that the proposed structure brings about 2.3 dB performance improvement at a bit error rate (BER) equal to 10-5over conventional LDS-OFDM while keeping the complexity affordable. Simulations for different scenarios also show that the LDS-OFDM outperforms similar well-known multiple access techniques such as multi-carrier code division multiple access (MC-CDMA) and group-orthogonal MC-CDMA.

Energy efficiency has become increasingly important in wireless communications, with significant environmental and financial benefits. This paper studies the achievable capacity region of a single carrier uplink channel consisting of two transmitters and a single receiver, and uses average energy efficiency contours to find the optimal rate pair based on four different targets: Maximum energy efficiency, a trade-off between maximum energy efficiency and rate fairness, achieving energy efficiency target with maximum sum-rate and achieving energy efficiency target with fairness. In addition to the transmit power, circuit power is also accounted for, with the maximum transmit power constrained to a fixed value. Simulation results demonstrate the achievability of the optimal energy-efficient rate pair within the capacity region, and provide the trade-off for energy efficiency, fairness and maximum sum-rate.

Amplify-and-forward (AF) is one of the most popular and simple approaches for transmitting information over a cooperative multi-input multi-output (MIMO) relay channel. In cooperative communication, relays are employed for improving the coverage or enhancing the spectral efficiency, especially of cell-edge users. However, in a multi-cell context, the use of relays will also lead to an increase in the level of interference that is experienced by cell-edge users of neighboring cells. In this paper, two novel precoding schemes are proposed for mitigating this adverse effect of cooperative communication. They are designed by taking into account the effect of interference coming from neighboring cells, i.e. other cell-interference (OCI), in order to maximize the sum-rate of cell-edge users. Our novel OCI-aware precoding schemes are compared against non OCI-aware techniques and results show the large performance gain in terms of sum-rate that our schemes can achieved, especially for large numbers of users and/or antennas in the multi-cell system.

We provide an analytical formula to evaluate the performance of the uplink of planar cellular networks when joint processing is enabled among limited number of base stations in a generalised fading environment. Focusing on user transmission power allocation techniques to mitigate inter-cluster interference we investigate the system's spectral-energy efficiency trade-off. The paper addresses the gains in both cell throughput and transmissions energy efficiency due to the combined strategies of base station cooperation and user power management. We assess the effect of the propagation environment and of the key network design parameters of cooperation cluster size and inter-site distance on the overall performance providing numerical results for a real-world scenario.

In this paper, we consider the precoding problem in the nonregenerative dual hop multi-input multi-output (MIMO) relay system. We propose a joint beamforming and power allocation method for a limited feedback system where a codebook-based beamformer is considered for each hop. The destination node selects the optimal beamforming codeword by relying on full channel knowledge of both source-relay and relay-destination channels for each hop from the code book and also compute the optimal power allocation coefficients for each substream. The index of the codewords and a quantized version of the power allocation coefficients are conveyed back to the source and relay nodes. The source and relay use the selected beamforming matrices and power allocation values to precode the data stream. In order to demonstrate the effectiveness of the proposed method, the performance of our joint beamforming and power allocation method is compared with previous codebook-based algorithms.

In this paper, we analyze the Hybrid Automatic Repeat re-Quest (HARQ) protocols used in conjunction with hybrid relaying schemes from the energy efficiency perspective. In cooperative communications, hybrid relaying strategy allows the relay to dynamically switch between different forwarding schemes according to its decoding status and provide either transmit or receive diversity to the users depending on the current channel condition. The energy efficiency analysis takes the circuitry energy consumption of all involved nodes into consideration and the energy efficiency is optimized in terms of energy per bit by manipulating the activation time and the transmission energy.

In this paper, we propose novel Hybrid Automatic Repeat re-Quest (HARQ) strategies used in conjunction with hybrid relaying schemes, named as H2-ARQ-Relaying. The strategies allow the relay to dynamically switch between amplify-and-forward/compress-and-forward and decode-and-forward schemes according to its decoding status. The performance analysis is conducted from both the spectrum and energy efficiency perspectives. The spectrum efficiency of the proposed strategies, in terms of the maximum throughput, is significantly improved compared with their non-hybrid counterparts under the same constraints. The consumed energy per bit is optimized by manipulating the node activation time, the transmission energy and the power allocation between the source and the relay. The circuitry energy consumption of all involved nodes is taken into consideration. Numerical results shed light on how and when the energy efficiency can be improved in cooperative HARQ. For instance, cooperative HARQ is shown to be energy efficient in long distance transmission only. Furthermore, we consider the fact that the compress-and-forward scheme requires instantaneous signal to noise ratios of all three constituent links. However, this requirement can be impractical in some cases. In this regard, we introduce an improved strategy where only partial and affordable channel state information feedback is needed.

The mutual information (MI) of multiple-input multiple-output (MIMO) system over Rayleigh fading channel is known to asymptotically follow a normal probability distribution. In this paper, we first prove that the MI of distributed MIMO (DMIMO) system is also asymptotically equivalent to a Gaussian random variable (RV) by deriving its moment generating function (MGF) and by showing its equivalence with the MGF of a Gaussian RV. We then derive an accurate closed-form approximation of the outage probability for DMIMO system by using the mean and variance of the MI and show the uniqueness of its formulation. Finally, several applications for our analysis are presented.

In this paper we provide a geometric and mathematical model that can be used to evaluate the user rate distribution for a cellular system under the notion of a hyper-receiver incorporating realistic system parameters. Variable cell sizes and different location-based decoding orders are analysed and the uplink user rate distribution of a cellular system in which each transmitted signal experiences a distance dependent path loss, fast fading and slow fading, is derived. Interestingly enough, among the three different decoding orders examined, the forward one provides the best results both in terms of fairness (larger percentage of users get satisfactory rates) and minimum rate. The difference among the decoding orders becomes even more notable as the cell sizes increase. There has also to be noted that none of these decoding orders affect the sum-rate.

We derive an analytical formula for the sum rate of the uplink of a linear network of cells when clustered joint processing is adopted among the base stations in a generalised fading environment. An inter-cluster interference allowance scheme is considered and various user power allocation profiles are investigated in terms of optimal achievable sum rate to highlight that cell-based power allocation is preferable to cluster-based. The contribution of each base station on the cluster sum rate is investigated and its importance is discussed. Numerical results are produced for a real-world scenario showing how medium density systems are the most viable case for clustered system design by achieving > 80% of the global cooperation capacity.

Efficient use of available spectrum is of concern to future wireless network planners. Although global cooperation at access points (APs) maximizes sum rate, for large networks this assumption is too complex to implement. We partition the wireless network into localized jointly decoded cells implemented as fixed size clusters. This is an alternative model which is more practical and improves efficiency of current systems. Conventionally, frequency allocation using interference avoidance maximizes spectrum usage. However, with clusters, careful allocation of interference needs to be explored. This is done using flexible bin based frequency allocation and applying heuristic tools. This work is the first known attempt to analyze uplink capacity of bin based fixed cluster cellular systems using genetic algorithms. To implement this, we derive an expression for the uplink capacity of bin based fixed clusters. We then input this as a fitness function to a modified simple genetic algorithm to compute a good fit for our bin allocation problem. We deduce that for sparsely distributed APs and large cluster sizes, rates close to that of a joint processor are achievable. Moreover, decreasing AP density for small cluster sizes (inter cell distance greater than 5 km for 7 cell-cluster) has insignificant effect on sum rate performance. However, with a nominal increase in the number of bins available for transmission, for dense system, the per-cell sum rate of a clustered cellular system can reach close to that of a hyper receiver using a genetic algorithm.

A novel joint decompression and forward error correction (FEC) decoding structure for a compress-and-forward relay system is proposed. We notice the possibility of iterative processing between the decompressor and the FEC decoder for the original source information and propose a turbo-like structure to allow interaction and extrinsic information exchange between these two parts. Simulation results show considerable gains through this interaction.

Reducing the consumed energy in wireless communication systems has a direct impact on operational expenditure as well as CO2 emissions. With increasing interest in multimedia applications and high data rate services, environmentally sustainable communications networks must reduce the energy per delivered bit at an equal rate, if not better. This paper addresses downlink energy-efficient transmission in OFDMA systems and maximizes the overall bits transmitted per joule of energy. In addition to the transmit power, circuit power is also accounted for in the energy-efficient design, which is tackled using both standard optimization techniques and a frame work based on time-sharing. Simulation results show similar performances for both cases with the latter having lower complexity and taking less CPU time to run.

A Hybrid ARQ (HARQ) scheme employing a flexible amplify and forward (AF) relaying is considered for a cooperative relay channel. Two phase types with flexible length: one phase for relay reception and another phase for relay forwarding are assumed to accommodate half duplex relaying. We assume two types of encoding: repetition coding (RC) and unconstrained coding (UC). The outage performance of the considered flexible AF scheme is analytically derived for any number of retransmissions, and both RC and UC encoding used by the considered HARQ. The state transition models of the considered protocols are presented and then the HARQ throughput and latency performance are analytically calculated; As a result time consuming Monte Carlo based evaluations are avoided. The provided analysis enables us to predict the performance and adjust transmission rate and frame structure for any combination of the signal to noise ratio (SNR) of the involved links. Performance gains of up to 1 and 1.5 dB are observed for the considered simulation scenarios thanks to the flexible AF combined with properly designed HARQ protocols. Also the flexible AF is able to attain its performance over all the range of SNRs of the constituent links while the conventional AF is only efficient on a restricted range of SNRs.

Amplify-and-forward (AF) is one of the most common and simple approaches for transmitting information over a cooperative multi-input multi-output (MIMO) relay channel. It has recently been demonstrated that the spectral efficiency of AF scheme can be maximized by using the relay as a smart precoder. However, source node precoding has not been included in the overall maximization problem. In this paper, we propose a joint precoder design at the relay and source nodes for maximizing the cooperative mutual information (MI), i.e., the combination of direct and relay link MI, and thus, for further improving the spectral efficiency of AF scheme. In addition, we provide an algorithm for performing our joint precoding technique. Performance analysis indicates that our novel precoding algorithm outperforms other existing AF precoding methods in various link configurations.

Amplify-and-forward (AF) is one of the most popular and simple approaches to transmit information over a cooperative multi-input multi-output (MIMO) relay channel. In this paper, we propose three novel power allocation methods for the downlink of cooperative multi-user MIMO AF system, which are designed to maximize the weighted sum-rate (WSR) of the cooperative system, by considering two different levels of channel state information (CSI). We design efficient precoding algorithms at the relay by assuming that either only the receive CSI or both receive and transmit CSI is available at the relay. Results show the performance improvement that our schemes can achieve in terms of sum-rate and WSR metrics.

In this paper we consider the uplink of a cellular network partitioned into localized jointly decoded cells. These jointly decoded cells are implemented as fixed size clusters. Such networks have a potential for real world deployments with improved spectral efficiency and user experience. Similar to conventional cellular networks, frequency planning can be considered as an efficient method to control interference between cells belonging to different clusters. Here we consider frequency planning in the form of allocating set of frequency bins to cells within clusters. As service providers are more interested in providing QoS, the considered bin allocation apart from maximizing system throughput, should also allocate cell resources in a fair manner. We propose a new cell based QoS balancing function which helps to maximize sum rate as well as achieve cell based fairness using both coupled and decoupled power allocation schemes. To implement this function, we use SIC in order to derive cell based sum rate. The derived formulation is conditioned for both hard and soft fair1ness constraints. This is then applied as input to a Genetic Algorithm in order to optimize the derived network wide QoS balancing function. Numerical results indicate that under wide range of bandwidth conditions, and in densely located cells employing decoupled power allocation, resources are more fairly allocated than in cells employing coupled power allocation.

Multicell joint processing has been shown to efficiently suppress inter-cell interference, while providing a high capacity gain due to spatial multiplexing across distributed Base Stations (BSs). However, the complexity of the optimal joint decoder in the multicell uplink channel grows exponentially with the number of users, making it prohibitive to implement in practice. In this direction, this paper investigates the uplink capacity performance of multicell joint linear minimum mean square error (LMMSE) filtering, followed by single-user decoding. The considered cellular multiple-access channel model assumes both Rayleigh and Rician flat fading, path loss, distributed users and correlated multiple antennas at the base station side. The case of Rayleigh fading is tackled using a free probability approach, while the case of Rician fading is addressed through a deterministic equivalent calculated using non-linear programming techniques. In this context, it is shown that LMMSE can provide high spectral efficiencies in practical macrocellular scenarios.

In this paper LDS-OFDM is introduced as an uplink multicarrier multiple access scheme. LDS-OFDM uses Low Density Signature (LDS) structure for spreading the symbols in frequency domain. This technique benefits from frequency diversity besides its ability of supporting parallel data streams up to 400% more than the number of subcarriers (overloaded condition). The performance of LDS-OFDM is evaluated and compared with conventional OFDMA systems over multipath fading channel. Monte Carlo based simulations for various loading conditions indicate significant performance improvement over OFDMA system.

In this paper, multilevel coding is tailored for cooperative communication, where the source deploys a layered encoding structure. Due to the BER difference for different coding levels, there is some possibility that the relay, despite of successful decoding in upper coding levels, might not be able to correctly decode in lower levels. We propose a hybrid relaying scheme to cope with this problem, where the relay deploys decode-and-forward in upper levels and compress-and-forward in lower levels. Simulation results demonstrate that this hybrid technique approaches a fine balance among the complexity, BER performance and transmission efficiency.

In the information-theoretic literature, it has been widely shown that multicell processing is able to provide high capacity gains in the context of cellular systems and that the per-cell sum-rate capacity of multicell processing systems grows linearly with the number of Base Station (BS) receive antennas. However, the majority of results in this area has been produced assuming that the fading coefficients of the MIMO subchannels are totally uncorrelated. In this direction, this paper investigates the ergodic per-cell sum-rate capacity of the MIMO Cellular Multiple-Access Channel under correlated fading and multicell processing. More specifically, the current channel model considers Rayleigh fading, uniformly distributed User Terminals (UTs) over a planar cellular system and power-law path loss. Furthermore, both BSs and Uts are equipped with correlated multiple antennas, which are modelled according to the Kronecker model. The per-cell sum-rate capacity closed form is derived using a Free Probability approach and numerical results are produced by varying the cell density of the system, as well as the level of correlation.

Two Hybrid ARQ (HARQ) schemes based on selective decode and forward are considered for a cooperative half-duplex relay channel. Two time slot types: T1slot for relay listening and T2slot for relay forwarding are assumed to accommodate half duplex relaying. The considered HARQ schemes differ in the frequency of the ARQ feedback: one is frame and the other is slot based where each frame is composed of one T1followed by one T2slot. Two types of encodings: repetition coding (RC) and unconstrained coding (UC) (also known as incremental redundancy) are assumed. Outage performance analysis is carried out for both RC and UC. The state transition models of the considered protocols are presented and are used to analytically calculate the HARQ throughput and latency performance; thus avoiding time consuming Monte Carlo based evaluations. The provided analysis enables us to predict the system performance and tune its transmission parameters (transmission rate and frame structure) for any combination of the signal to noise ratio (SNR) of the constituent links.

In this paper, we consider a three-node relay system with a hybrid relaying scheme, where the relay, based on its decoding status, switches between decode-and-forward (DF) and compress-and-forward (CF) adaptively. We propose according HARQ strategy and analyze its throughput performance. Then, we consider practical implementation issues by enhancing the ability of the feedback channel from the destination to the relay to convey a few extra bits (only 2 bits in this paper) and propose a modified HARQ scheme accordingly. The combined technique exhibits superior performance over direct transmission and conventional DF.

Multicell joint decoding has been proven to greatly enhance the capacity of cellular systems in a range of regimes. However, the complexity of such a joint receiver makes it impossible to implement in practice using current computational capabilities. In this direction, this paper investigates the capacity performance of reduced-complexity communication schemes in order to evaluate their performance with respect to the optimal multicell joint decoding scheme. More specifically, two sub-optimal schemes are considered: 1) intra-cell user orthogonalization combined with optimal multicell joint decoding and 2) intra-cell user orthogonalization combined with linear MMSE filtering and single-user decoding. The employed cellular multiple-access channel model incorporates flat fading, path loss, distributed users and multiple antennas at the Base Station, while both peak and average transmit power constraints are taken into account. In this context, it is shown that linear MMSE filtering combined with multiple BS antennas and intra-cell orthogonalization can still provide a considerable capacity enhancement. Furthermore, FDMA is shown to be more efficient than TDMA as an intra-cell orthogonalization technique.

We noticed that in a relay system, the assumption of global Channel State Information (CSI) knowledge is unrealistic and normally, only the receiver but not the transmitter side has CSI knowledge. In this paper, we analyzed, with receive CSI, the performance of hybrid relaying scheme in the half-duplex relay channel in terms of the outage probability and expected throughput, where the relay switches between decode-and-forward (DF) and compress-and-forward (CF) modes adaptively according to the current channel realizations. Moreover, since the original CF technique requires global CSI at the relay to calculate the optimal compression rate, we established a restricted feedback link to convey extremely limited CSI (only 3 bits in our results) from the destination to the relay and develop a more practical hybrid relaying scheme. Simulation results revealed that the hybrid relaying scheme with restricted feedback outperforms DF especially when the link between source and relay is of low quality.

In the ergodic capacity literature, the majority of results preserve the assumption of a flat-fading Gaussian channel. However, the actual wireless channels in current communication systems are often wideband and therefore time dispersive and frequency selective. In this direction, we study the ergodic capacity of a wideband MIMO channel. Starting from a tapped delay line model for the time domain, the frequency domain model is derived by employing the Fourier transform. However, in both cases the resulting channel matrix is characterised by non-separable correlation amongst the Gaussian blocks. The asymptotic eigenvalue probability density function and the channel capacity are calculated by specializing a theorem originating in operator-valued free probability. Finally, numerical results are presented to verify the validity of the approach and study the effect of the channel model parameters.

In this paper we propose a novel flexible amplify and forward (AF) relaying protocol with different duplexing ratios. We show that the average throughput can be considerably improved by properly adjusting the duplex ratio. Here it is considered that the transmitted and received channel state information (CSI) are available at the relay. We introduce a new processing technique at relay for above case in order to achieve higher throughput and lower bit error rate (BER) than traditional schemes. Also BER upper bounds for our presented cooperative model are derived.

Decode-and-forward (DF) is one of the most popular approach to transmit information over a cooperative relay channel. In DF, information coming from different sources is simply combined regardless of their respective link qualities, and thus DF is not optimized for any propagation conditions. In this paper, we propose a novel transmit cooperation scheme that exploits asymmetric link qualities by using layered higher order modulation. A partial forwarding approach is followed by taking advantage of the layered structure: one part of the information is forwarded by a relay for increasing the robustness of the direct link and the rest of the information flows through the boosted direct link. Moreover, our scheme is based on a distributed serially concatenated encoding structure that can accommodate iterative decoding to further improve its performance. The complexity of our scheme is seemingly identical to DF scheme. Performance evaluation shows that our scheme provides a better spectral efficiency in asymmetric propagation conditions than DF scheme for both non-iterative and iterative decoding.

Optimum decoding of the cooperative full decode and forward (DF) scheme is derived. It is shown that optimum decoding requires marginalization of a so called partially observed likelihood function over all relay decoder outcomes. Bhattacharyya bound on relay decoding error is used to fully factorize the partially observed likelihood function. The full factorization will allow efficient marginalization over the joint source-relay code space. A tight analytical error bound is derived that its computation further requires efficient tools to compute weight structure of the joint source-relay code. For a simple (7,4) Hamming code under fast fading condition the derived optimum decoder significantly outperforms the conventional decoder. The optimum decoder is more robust to weak source-relay link conditions.

A model that effectively captures the relay decoding error is proposed for a distributed turbo code (DTC) over a cooperative relay channel. The model consists of a memoryless binary symmetric channel (BSC) placed before the relay encoder, hence called pre-BSC. Accordingly the required iterative decoder is derived that consists of an extra update function to be applied on extrinsic information before their exchange. The derived update function is in form of a smooth clipping and therefore the overall decoder is called clipped iterative decoder (clipped ED). Clipped ID is robust to the relay decoding error and is able to significantly improve the final performance, especially when source-to-relay link becomes erroneous.

In this paper we study the effect of Base Station (BS) and User Terminal (UT) on the capacity of the Gaussian Cellular Multiple Access Channel. We also build a Monte Carlo simulator using realistic system parameters and distance dependent shadowing correlation estimation models. We are able to properly verify the theoretical analysis and we provide an insight on the maximum achievable capacity for real cellular systems.

In this paper we derive the sum rate of the uplink of a linear network of cells when clustered coordinated processing is adopted among the base stations in a generalised fading environment. Various cluster isolation schemes along with an interference allowance scheme are analysed and compared in terms of achievable sum rate with each other and to the optimum case of a system with central processor. Numerical results are produced for a real-world scenario.

When channel state information (CSI) is not available to the transmitter, outage events might happen and automatic repeat request (ARQ) is implemented to ensure reliable transmission in such case. In this paper, we consider a three nodes relay system with hybrid relay scheme, where the relay, based on it decoding status, could switch between decode-and-forward (DF) and compress-and-forward (CF) adaptively. We notice that CSI is required when CF is deployed and consider practical implementation issues by enhancing the ability of feedback channel from the destination to the relay to convey a few extra bits (only 2 bits in this paper) in addition to the ACK/NACK bit and propose a new ARQ scheme. The modified scheme allows the relay to utilize various relay schemes more flexibly according to its coding status and the extra feedback bits. ARQ strategies with hybrid relay schemes exhibits superior performance over direct transmission and pure DF, especially when the relay is close to the destination.

In this paper, we extend a well-developed quantization scheme to block fading relay system using compress-and-forward and propose a new achievable rate based quantization scheme (ARBQS). A new signal combination scheme with less complexity is also proposed accordingly. Based on the scalar quantizer obtained, vector quantizer with Trellis coded quantization (TCQ) scheme is provided. While many quantization schemes have concentrated on minimization of quantization distortion, our simulations results indicate that the new scheme achieves better performance in both AWGN case and block fading case without distortion minimization and achieve higher compression efficiency and reduced complexity simultaneously.

Automatic Repeat re-Quest (AQR) is implemented to ensure reliable transmission when channel state information (CSI) is not available to the source and the selected transmission rate is not supported by the current channel realization. We consider a relay system with hybrid relay scheme, where the relay switches between decode-and-forward (DF) and compress-and-forward (CF) adapting to the decoding status. In such case, we propose new ARQ strategy and analyze its performance in terms of maximum throughput, average reward and inter-renewal time. Compared with pure DF, the hybrid relay schemes show considerable gain.

In the context of cellular systems, it has been shown that multicell processing can eliminate inter-cell interference and provide high spectral efficiencies with respect to traditional interference-limited implementations. Moreover, it has been proved that the multiplexing sum-rate capacity gain of multicell processing systems is proportional to the number of base station (BS) antennas. These results have been also established for cellular systems, where BSs and user terminals (UTs) are equipped with multiple antennas. Nevertheless, a common simplifying assumption in the literature is the uncorrelated nature of the Rayleigh fading coefficients within the BSUT MIMO links. In this direction, this paper investigates the ergodic multicell-processing sum-rate capacity of the Gaussian MIMO cellular multiple-access channel in a correlated fading environment. More specifically, the multiple antennas of both BSs and UTs are assumed to be correlated according to the Kronecker product model. Furthermore, the current system model considers Rayleigh fading, uniformly distributed UTs over a planar coverage area and power-law path loss. Based on free probabilistic arguments, the empirical eigenvalue distribution of the channel covariance matrix is derived and it is used to calculate both optimal joint decoding and minimum mean square error (MMSE) filtering capacity. In addition, numerical results are presented, where the per-cell sum-rate capacity is evaluated while varying the cell density of the system, as well as the level of fading correlation. In this context, it is shown that the capacity performance is greatly compromised by BS-side correlation, whereas UT-side correlation has a negligible effect on the system's performance. Furthermore, MMSE performance is shown to be greatly suboptimal but more resilient to fading correlation in comparison to optimal decoding.

The log-normal probability distribution has been commonly used in wireless communications to model the shadowing and, recently, the small-scale fading for indoor ultrawideband (UWB) communications. In this paper, a tight closed-form approximation of the ergodic capacity over log-normal fading channels is derived. This expression can be easily used to evaluate and compare the ergodic capacities of communication systems operating over log-normal fading channels. We also utilize this expression to show that the capacity of a multi-antennas UWB system operating over the IEEE 802.15.3a channel can be improved mainly through receive diversity.

The log-normal probability distribution is commonly used in wireless communications to model the shadowing and, more recently, the small-scale fading for indoor ultra-wideband communications. In this paper, an accurate closed-form approximation of the ergodic capacity over log-normal fading channels is derived. This expression can be easily used to evaluate and compare the ergodic capacity of communication systems operating over log-normal fading channels.

A generic cooperative BICM system is described and an analytical model capturing relay error through a binary symmetric channel (BSC) is presented. The analytical model is called Post-BSC model as the BSC channel is placed after encoder of the relay node. Tight BER upper bound is derived for the presented model and close match between simulation and analysis for the presented model is observed. However it is also observed that the proposed model is optimistic and fails to effectively model the original system at low SNR conditions of the source to relay link. Despite this fact the incorporation of the Post-BSC model based maximum likelihood decoding greatly improves the system BER with respect to the original DF scheme.

A generic cooperative MIMO BICM system is described. Achievable rates are computed based on the extended equivalent binary input channel model of the original BICM system. Full decode and forward is assumed at the relay node. Two types of two-phased transmission/reception protocols are employed to establish orthogonal transmission/reception of the relay node. The achievable rate results are provided for different combinations of modulation orders and the number of antennas used at the source and relay nodes. Quantitative results provided in this paper could serve as a guide on when to engage cooperative transmission and how to choose proper constellations and puncturing ratios for the practical BICM coded systems. Comparison of the considered BICM system with other possible cooperative coded systems is also crucial that this paper due to lack of space for exposition misses to address.

A novel approach for extension of soft decode and forward strategy into higher order MQAM modulation is proposed. A new soft mapping function is introduced to map soft bits onto a point in the complex plane. It is shown that the proposed soft decode and forward (SDF) scheme attains the same level of diversity as amplify and forward (AF) scheme while improves the overall system spectrum efficiency through forwarding with higher order modulations. Simulation results show that new scheme outperforms DF for different links conditions.

In this paper, we analyze the block error rate (BLER) and bit error rate (BER) of soft decode-and-forward (SDF) using distributed Turbo codes, which is proposed recently to mitigate error propagation caused by decoding error in the relay node. Union bound (UB) in fading channels is derived and compared with simulation results. In order to get tight bounds for block fading case, limit-before-average technique is used. Furthermore, we extend our analysis to the space-time cooperation framework. The analysis and simulation show that the derived bound is very tight.

It has been pointed out that Slepian-Wolf (SW) coding is efficient to compress data with side information available at the receiver. However, most papers assume that the compressed information is perfectly known to the receiver. In this paper, we consider more practical assumptions that the channel between the relay and the destination is not perfect and error protection need to be implemented. Accordingly, a soft Slepian-Wolf decoding structure is proposed. The new structure not only supports soft Slepian-Wolf decoding within one level, but it also allows soft information passing between different levels. We also consider the relationship between the codes for error protection and the codes for compression and propose a joint decoding and decompressing algorithm to further improve the performance.

This paper studies the area of link adaptation for multicarrier code division multiple access (MC-CDMA) radio interface and adapts the rate and transmission power jointly over temporal as well as spectral domains. On one side, frequency domain spreading lends a high degree of frequency diversity to MC-CDMA. On the other, it has been identified as the main hurdle when it comes to spectral domain rate allocation in MC- CDMA This paper presents band based MC-CDMA (BB-MC- CDMA) architecture as an efficient scheme to practically realize the spectral domain rate allocation in MC-CDMA without undergoing the drawbacks of other published techniques for this purpose. BB-MC-CDMA asks for the elimination of frequency interleaving, usually considered to be an essential ingredient of MC-CDMA. It also suggests an intelligent reduction in the spreading factor in a channel aware fashion. Furthermore, based on BB-MC-CDMA architecture, joint rate and power adaptation over time and frequency (JRPATF) has been shown to outperform the frequency domain power allocation only.

Timing and frequency synchronisation for the uplink of OFDMA systems is discussed. The uplink synchronisation procedure is presented and a novel timing and frequency offset estimation scheme is proposed. The timing and frequency offsets are estimated by identifying the differential phases of the training subcarriers in frequency and time dimensions, respectively. The frequency offset is estimated ahead of the timing offset, after which intercarrier interference compensation is carried out based on the estimated frequency offset. Finally, the timing offset is estimated after eliminating the frequency offset's influence. The principle of best linear estimation is applied. Both the case of a single user and that of multiple users simultaneously accessing the network are considered. In contrast to other methods, the proposed scheme has moderate complexity and allows flexible subcarrier assignment schemes. The analyses and simulation results demonstrate the accuracy of the proposed scheme in the uplink channels.

Novel low-density signature (LDS) structure is proposed for synchronous code division multiple access (CDMA) systems for an uplink communication over AWGN channel. It arranges the system such that the interference pattern being seen by each user at each received sampled chip is different. Furthermore, new near-optimum chip-level iterative multiuser decoder is suggested to exploit the proposed structure. It is shown via computer simulations that, without forward error correction (FEC) coding, the proposed LDS structure could achieve near single-user performance with up to 200% loading condition. As the proposed iterative decoding converges relatively fast, the complexity is kept much more affordable than that of optimum multiuser detection (MUD) with conventional structure.

This paper studies adaptive power allocation among sub-carriers in MC-CDMA. Due to intrinsic nature of MC-CDMA; carrier based power allocation schemes cause MAI (multiple access interference) enhancements, hence fail at higher system loads. We propose a band based dynamic link adaptation (BBDLA) scheme that preserves orthogonality (among users) by spreading user's signal only over a band of adjacent N sub-carriers (Nc) of the channel. Hence, it allows band based power allocation without causing any MAI. However, with only N orthogonal users supported on a particular band, BBDLA essentially proposes a hybrid of FDMA with MC-CDMA where Bands and transmit powers are optimally assigned to users by base station (in accordance with their channel state). Optimum band allocation for BBDLA is found to be computationally intractable hence a sub-optimal heuristic approach is proposed with equal power distribution among all assigned bands for each user. Effect of Bcover choice of N is studied and BBDLA with suitably chosen N, is shown to outperform other published carrier based power allocation schemes while it maintain almost single user BER performance up to 62% of full system loading.

Recently, the notion that a logical next step towards future mobile radio networks is to introduce multihop relaying into cellular networks, has gained wide acceptance. Nevertheless, due to the inherent drawbacks of multihop relaying, e.g., the requirement for extra radio resources for relaying hops, and the sensitivity to the quality of relaying routes, multihop cellular networks (MCNs) require a well-designed radio resource allocation strategy in order to secure performance gains. In this paper, the optimal radio resource allocation problem in MCNs, with the objective of throughput maximization, is formulated mathematically and proven to be NP-hard. Considering the prohibitive complexity of finding the optimal solution for such an NP-hard problem, we propose an efficient heuristic algorithm, named integrated radio resource allocation (IRRA), to find suboptimal solutions. The IRRA is featured as a low-complexity algorithm that involves not only base station (BS) resource scheduling, but also routing and relay station (RS) load balancing. Specifically, a load-based scheme is developed for routing. A mode-aware BS resource-scheduling scheme is proposed for handling links in different transmission modes, i.e., direct or multihop. Moreover, a priority-based RS load balancing approach is presented for the prevention of the overloading of RSs. Within the framework of the IRRA, the above three functions operate periodically with coordinated interactions. To prove the effectiveness of the proposed IRRA algorithm, a case study was carried out based on enhanced uplink UMTS terrestrial radio access/frequency-division duplex with fixed RSs. The IRRA is evaluated through system level simulations, and compared with two other cases: 1) nonrelaying and 2) relaying with a benchmark approach. The results show that the proposed algorithm can ensure significant gains in terms of cell throughput

In this paper, an integrated radio resource allocation (IRRA) algorithm is proposed for enhanced uplink UTRA-FDD with fixed relay stations (RSs). It comprises three entities: load based route manager (LBRM), base station resource scheduler (BSRS), and relay station load balancer (RSLB). LBRM is responsible for the selection of user transmission routes, BSRS is for the scheduling of user transmission time and rates based on the available base station (BS) capacity, and RSLB is for the fine-tuning of user resource assignments (e.g. assigned rates) so as to prevent the overloading of RSs. The three entities operate periodically, synchronously, and with coordinated interactions. By system level simulations, the proposed algorithm is evaluated and compared with two other cases: 1) non-relaying, 2) relaying with a benchmark approach. The results show that IRRA can ensure significant gains in terms of cell throughput.

One of the key research issues in wireless systems is how to improve the system capacity. MIMO has been proven as an effective method to achieve this. Previously, the focus of MIMO-OFDM research in high performance metropolitan area network (HIPERMAN) systems was on space time coding (STC) and beamforming. Recently, multi-user detection (MUD) has emerged as a novel approach in MIMO-OFDM-based HIPERMAN systems. In this paper, we have proposed a new MAC design, which includes the new and flexible MAC frame structure and an efficient dynamic resource allocation algorithm, in order to accommodate the MUD techniques in uplink transmission in HIPERMAN systems. The performance of the new MAC design has been evaluated via simulation means. The simulation results show that the new MAC design based on MUD can significantly increase the system capacity.

SIR estimation for fast closed loop power control (CLPC) of a WCDMA FDD downlink with space time transmit diversity (STTD) is analysed. It is shown that without STTD encoding/decoding of the DPCCH (dedicated physical control channel) pilot symbols of the two antennas, the SIR estimation suffers from inter-antenna interference. Without modifying the DPCCH pilot patterns in the current 3GPP standard, near-best performance is achieved by using all the pilot symbols for signal power estimation, but only the STTD decoded shaded symbols for interference estimation, to avoid the inter-antenna interference.

We study the choice of block interleavers in a MIMO-OFDM based broadband fixed wireless access system for the HIPERMAN and IEEE 802.16a standards with space-frequency trellis coding under typical channel conditions. It has previously been shown that a given code offers varying levels of error performance depending on the degree of frequency selectivity of the channel. Code performance was comparatively better in channels with higher frequency selectivity or delay spreads, while performance was particularly degraded in channels with low frequency selectivity. In order to extract the maximum possible frequency diversity and close this gap in performance, we investigate the use of appropriate interleavers. As different channels favour interleavers of different depths, we recommend suitable interleaver depths for the typical channels considered. With these interleavers the performances can be significantly improved and can be made comparable despite the variation in channel frequency selectivity.

Uplink and downlink load equations for a snapshot of users in a UMTS network are presented in unified and general matrix form. Capacity and coverage constraints of the system are presented in the form of inequalities to he satisfied by users and network loadings. It is shown that the static simulation of the network is the joint solution of the load equations and capacity and coverage constraints carried out with an iterative method.