To detect the position and the orientation of a mobile device within a Wireless Local Area Network (WLAN) covered by multiple access points (APs), the intrinsic properties of multiple-input multiple-output (MIMO) channels are used linking the received signal strength indicators (RSSIs) to the distance and exploiting the received signal correlation structures. Location and orientation fingerprinting is a map based positioning solution that stores for a given orientation past measurements of RSSIs at known reference/grid points in a database that is later used to localize a mobile device at an unknown location and with unknown orientation to the closest reference point. This paper focuses on processing the RSSI data vectors from multiple receiving antennas on a downlink by applying the core tools of Machine Learning (ML) classification methods to evaluate the effects of MIMO RSSI meta-data when capturing 802.11n/ac packets using commodity hardware. Specifically, the paper provides insights into the design of the overall location fingerprinting system operating with new WiFi physical link layer protocols. To verify the operation of the proposed system, experimental results are presented to investigate the impact of different factors, like the number of receive antennas, affecting the estimation accuracy for the location and the orientation of mobile user.

This paper introduces modulation and coding schemes which encode data into beams of antenna arrays by exploring the angular models of wireless channels. First, the paper presents Generalized Beam Angle Channel Modulation (G-BACM) which maps the spatial symbols into multiple angles of wave propagation and arrival. Then, space-time block coding (STBC) strategies for G-BACM are investigated. In the case of G-BACM configuration with two simultaneous beams, the block of information bits is mapped into three symbols at the encoder: (i) one, spatial, symbol indexing two beams representing the angles of arrival of the two amplitude and phase modulated (APM) carrier signals and (ii) two APM symbols independently transmitted over two beams. Utilizing simultaneous transmissions on two or more beams improves the bandwidth efficiency and is also used to benefit the diversity aspect of the proposed system. Specifically, STBC strategies for G-BACM are presented where multiple copies of data streams are transmitted across a number of beams rather than antennas as in conventional multiple-input multiple-output (MIMO) systems. The performance of G-BACM with and without STBC is analyzed in multipath fading channels when trading-off between the system rate and reliability.

This paper considers network information flow in a multiple-input multiple-output (MIMO) wireless network with four users where (i) two primary users equipped with multiple antennas exchange independent messages via a half-duplex relay and (ii) two secondary users with single antenna transmit to and receive data from the relay. This asymmetric traffic flow problem is a specialized version of a multi-pair two-way relay channel where, in the multiple access (MAC) phase, four users send all messages to the relay simultaneously, and, in the broadcast (BC) phase, the relay transmits messages to users also on a single MIMO channel access. When spatially multiplexing two- and one-way data transmissions via a cooperating relay implementing decode-and-forward (DF) processing, the objective is to work with a minimized number of antennas at all nodes in the system. Specifically, this paper presents a design for precoding and nulling vectors in the proposed signal alignment (SA) scheme with zero- forcing (ZF) decoding. In this design, there is a single redundant antenna at the relay during the MAC phase, which is exploited to provide the diversity advantage. The optimum subset of receiving antennas at the relay is selected by a Max-Min criterion with respect to the post- processing SNR. Simulation results show an improvement in terms of BER when optimization is deployed during the antenna selection process.

This paper considers a layered transmission between the source and the destination aided by two half-duplex relays. In the proposed system, the single antenna source continuously broadcasts superposition coded (SC) base and enhancement layers, while relays, with one active antenna, retransmit in turn the enhancement layer. Using two antennas, the destination as well as the relays receive mixed base, enhancement, and delayed enhancement layers through over-the-air signal summation. To recover from inter-relay interference (IRI), the receiving relay decouples two spatial streams representing data of interest using the virtual Multiple Input Multiple Output (MIMO) channel from the source and the transmitting relay. Because of the network topology, the receiver deploys both virtual MIMO and Successive Interference Cancellation (SIC) techniques to first decode the delayed enhancement layer and then the delayed base layer. In this decode-and-forward (DF) transmission scheme, the transmissions from the source and the relays are aligned in time, power, and spatial domains to optimize the system throughput and reliability. Finally, this paper demonstrates that the SC with alternate relaying in the proposed single input multiple output (SIMO) setup has a better performance than similar conventional schemes.

This paper extends Beam Angle Shift Keying (BASK) transmission technique into a multi-user version called Beam Angle Multiple Access (BAMA). BASK is a recently developed antenna beam pattern modulation scheme where at the transmitter, the block of information bits is mapped into a spatial symbol selecting the beam for the unmodulated carrier signal. At the receiver, after specular reflections, the carrier signal arrives at the receiver from one direction over the duration of the spatial symbol and the receiver antenna array is used to detect single-user data through angle-of-arrival (AOA) estimation. In this paper, multiple access on the uplink is achieved by assigning subsets of beams to individual users signaling with BASK. At the base station, over the duration of the spatial symbol the receiver decides on a subset of possible multiple AoAs corresponding to synchronized spatial symbols from different users. Specifically, we propose a maximum-likelihood (ML) detector which can successfully decode incoming data from multiple simultaneous BASK transmissions by deploying a linear array of receive antennas. Unlike in spatial division multiple access where a fixed beam arrangement is used, BAMA detects the beams used by multiple users on a symbol-by-symbol basis. In the proposed scheme, the management and selection of beams are crucial with respect to capacity of the system. It is demonstrated that the detection reliability of the spatial symbols in BAMA is determined by the number of antennas used at the receiver and the actual angles of signal arrival.

This paper presents the integration of distributed space-time block coding (STBC) and signal alignment (SA) in multiple-input multiple-output (MIMO) Y channels where multiple terminals communicate with each other in a bi-directional manner via the relay. The objective is to take advantage of the STBC diversity gain without losing much of the high bandwidth efficiency in MIMO Y channel schemes with SA alone. The proposed deployment of STBC represents a form of cooperative coding between the terminals and is referred to as networked MIMO. Specifically, by a thoughtful design of pre-processing vectors and scheduling of transmissions, the signals with mutual information in bi-directional links between terminals are aligned into proper spatial dimensions according to the selected space-time block code. The transmission schemes are also optimized to reduce computational complexity and improve time slot utilization. It is demonstrated with simulations that the proposed design in a three-user MIMO channel offers significant coding gain of 25 dB at the bit error rate (BER) of 10-3over the conventional MIMO channel signaling in Rayleigh fading channels. This improvement is achieved at the expense of reducing the bandwidth efficiency by a factor of 7/2.

This paper introduces a novel transmission technique named Beam Angle Channel Modulation (BACM) that uses an antenna array to encode the information symbols into the angle of propagation (and arrival) wave in the wireless channel. At the encoder, the block of information bits is mapped into two symbols: (i) a spatial symbol selecting the direction of arrival of the amplitude and phase modulated carrier signal and (ii) a temporal symbol chosen from the constellation diagram like QAM or PSK. The proposed scheme follows the model for concatenated modulation designs like recently introduced spatial modulation (SM). The use of the transmitted signal angle through antenna array beamforming increases the spectral efficiency of the single-input single-output (SISO) conventional (temporal) modulation by the base-two logarithm of the number of spatial beams that can be resolved (detected) at the receiver. Direction-of-arrival type detection for spatial symbols is developed using a linear array of receive antennas. It is demonstrated that the detection reliability of the spatial symbols in BACM is determined by the number of antennas used at the receiver and the actual angles of signal arrival.

This paper considers the layered transmission between the source and the destination over two relays using superposition coding (SC). In this two-hop decode-and-forward (DF) relaying system, because of the network topology, the receiver continuously decodes only the base layer of the direct transmission from the source; the enhancement layer is decoded with a delay based on the transmission from one of the two relays sending and receiving in alternate time slots. Alternate relaying improves the spectral efficiency of the scheme, however it causes inter-relay interference (IRI), which may limit the system performance if not mitigated. To allow the proper data recovery at the relays and at the destination, we have designed successive interference cancellation decoding schemes that consider different power allocations to the base and enhancement layers. Specifically, based on the channel gains between different transmitter-receiver pairs, the transmissions from the source and the relays are aligned in time and power as to optimize the system throughput. Finally, based on the analytical derivations and simulations, we present numerical results for capacity improvements in the proposed scheme over the existing schemes.

This paper considers multi-way communications among three users equipped with multiple-input multiple-output (MIMO) transceivers that exchange massages between each other via two amplify-and-forward (AF) co-located relays. In this network with half-duplex MIMO relays, the wireless medium is simultaneously utilized for time-slotted transmissions by one of the users and one of the relays in order to increase the network capacity. The relays successively relay the signals creating inter-relay interference (IRI), which limits the bit error rate (BER) performance. To mitigate the IRI, this paper develops a cancellation technique at the receiving side of the users through specialized signal processing and scheduling of transmissions with opportunistic listening. The full IRI cancellation is possible assuming that every transceiver knows its receiving channel state information (CSI) and the inter-relay CSI. When all nodes - users and relays - are equipped with M antennas, the proposed scheme allows to exchange M messages per time slot which doubles the capacity of the network over the conventional AF system operating with a single relay in one-way setup. Simulation results document the effectiveness of the developed scheme in terms of channel capacity and the BER performance.

In this paper, we design a signal alignment scheme that exploits orthogonality of spatial signalling dimensions in the multiple-input multiple-output (MIMO) Y channel, where three users send messages to each other through a relay. The antenna configuration in the original MIMO Y channel system imposes limitations on controlling the minimum distance between signaling points representing network coded messages and affects symbol error rate performance. To mitigate this problem, this paper adds one redundant antenna at every user and designs the corresponding precoding vectors to obtain the flexibility in the selection of orthogonal signaling dimensions and to simplify the decoding at the relay. Specifically, as demonstrated through simulations, the design of precoding vectors in the proposed scheme for users improves the bit error rate (BER) performance but the BER is not balanced among the three users. We even the performances via power allocation applied to distribute energy among the users based on their channel conditions. In addition, iterative optimization of the signaling dimensions and time scheduling of transmissions according to channel states are employed to further improve the BER performance.

Abstract Because of the surging demands of multimedia services, quality‐of‐experience (QoE) is becoming an important metric to evaluate network quality from users' perspective. In this paper, resource optimisation to achieve optimal tradeoff between QoE and energy consumption in bidirectional orthogonal frequency‐division multiple‐access relaying networks is addressed so as to provide satisfactory multimedia delivery quality and support green communications. We first formulate a QoE‐energy efficiency tradeoff optimisation where QoE requirements and relaying traffic balance are considered and prove that QoE‐energy efficiency is quasiconcave on QoE, which suggests the existence of a unique global optimal tradeoff point. We then propose an optimisation framework to achieve the optimal tradeoff efficiently. With the framework, we develop resource allocation approaches for two specific relaying strategies, that is, two‐phase decode‐and‐forward relaying with dynamic XOR network coding and compute‐and‐forward relaying with physical network coding via structured codes. Numerical results validate theoretical findings and demonstrate the effectiveness of the proposed optimisation solution for achieving the tradeoff between QoE and energy consumption. Copyright © 2015 John Wiley & Sons, Ltd.

This paper considers amplify-and-forward (AF), multiple-input multiple-output (MIMO), two-hop relay systems in which the inter-relay interference (IRI), if not mitigated, may limit performance. In these systems with half-duplex relays, through TDMA scheduling, the wireless medium in both hops is always utilized through the simultaneous transmission of one of the sources and one of the relays which in turn leads to IRI. By representing IRI with the recursive term(s) and exploiting opportunistic listening, this interference is fully removed at the receiver(s) using limited channel state information (CSI) from both hops. As presented in this paper, the proposed MIMO IRI cancellation is applicable to cellular and ad-hoc wireless networks and could work with an arbitrary number of antennas provided that the number of antennas at the corresponding relays and the receivers is the same. We analyze the diversity gain and the multiplexing gain through simulations to verify the good performance of the proposed algorithm.

This paper presents our initial investigations of noise enhancement control when decoding uplink transmissions in multi-cell multiuser multiple- input multiple-output (MU-MIMO) systems with zero- forcing (ZF) post-processing. This problem has been partially addressed within simplified cellular system topologies and with single antenna terminals. However, applying existing solutions directly to a multi cell system is not viable due to the noise enhancement that would heavily affect the inter-cell interference (ICI). Therefore, this paper proposes a cross-layer resource allocation to improve the performance by utilizing a low complexity scheduling (user and antenna selection) and a power allocation method. The proposed scheduling algorithm extends our previous work to a multi cell system where the base and the mobile stations are equipped with multiple antennas. When allocating the power levels to different users in order to manage the multiple access interference (MAI) in MU-MIMO environment, we utilize Newton's method for resource optimization due to its efficiency in finding the combination of spatial streams and power levels to improve the average bit error rates (BERs) and their statistics for different users. This improvement in BERs is documented in terms of median and average BER performance in the system under study with and without centralized ICI cancelation.

In this paper, we propose a blind algorithm for channel identification and signal separation in MIMO OFDM systems with Nyquist sampling at the baseband. To estimate in time the channel and the input signals using compressed sensing, we exploit the sparsity structure of the matrix type channel impulse responses and the Gaussian characteristics of the transmitted OFDM signals. The matching pursuit sparse algorithm is applied in the channel recovery. First, we develop the method for blind deconvolution in SISO systems where after estimating the channel, a zero-forcing (Z-F) equalizer in the frequency domain recovers the transmitted QAM symbols. Then, we apply the method in the MIMO setting. This is accomplished by decomposing the matrix type convolution representing the mixing process in the MIMO time dispersive channel into systems of equations similar to the SISO case. Specifically, in the MIMO system, the SISO type sparse channel estimation is performed independently and in parallel for every receive antenna. The QAM symbol recovery on spatial streams is performed at every subcarrier using a matrix equivalent to the Z-F equalizer. The good estimation convergence of the method and its resilience in different SNR scenarios is verified through extensive simulations.

This paper investigates the performance of wireless network coding (NC) schemes for two-way relay channels with periodic transmissions. In particular, we consider a network with two source nodes and a single relay, with the latter broadcasting the XOR-ed version of the received data. Synchronization of transmissions to maximize the power saving periods in sleep mode and the assignment of transmit power values to minimize the total transmit power are examined considering practical constraints in the system. To test the ideas developed in real world environments, a communication protocol is implemented on CrossBow IRIS motes in TinyOS and its performance is characterized using power consumption and packet loss rates.

In this paper, we investigate the joint optimization of power allocation and subcarrier assignment in the OFDM bidirectional systems where two users exchange data assisted by multiple decode-and-forward (DF) relays. We assume the availability of imperfect channel state information (CSI) that contains a probabilistic uncertainty component and consider its worst effect when performing resource allocation. Moreover, we adopt dynamic network coding to exploit channel diversity. The objective of the resource allocation problem is to maximize the weighted sum rates of the two users subject to quality-of-service (QoS) requirements and individual power constraints. We formulate the problem as a mixed integer programming problem and solve it efficiently in an asymptotic manner by using the dual method. Simulation results show that the proposed scheme is robust to imperfect CSI and provides better performance compared to the scheme with static network coding.

When deploying network coding in a two-way data exchange via a relay, time asynchronism is a practical concern requiring special treatment. If two terminal nodes generate traffic flows with the same average rate and random arrival times, in order to use network coding based on XOR-ing of packets at the relay, there is a need to buffer the data which may lead to prohibitive delays. In this paper, to bound these delays, we propose to limit the number of packets that can be buffered at the relay by periodic flushing of the buffer. When times arise that there is/are no matched packet(s) for network coding at the relay and “single packet” broadcast(s) appears unavoidable, these opportunistic transmissions are used to send erasure coded packets to improve the reliability of the data exchange. In particular, three approaches which bound the delay at the relay before sending the erasure coded packets are investigated. The approaches are to either impose a time limit for buffering the packets, limit the number of network coded transmissions made before flushing the buffer or to flush the buffer after a specific number of packets have been received from any one source. Performance tradeoffs between erasure based improvements in Packet Loss Rates (PLRs), delays, energy conservation and throughput are documented for traffic with Poisson arrival times.

In the design of Wireless Sensor Networks (WSNs), energy conservation is a goal at all system levels, from the application down to the hardware. This paper focuses on network-level opportunities for energy conservation, with emphasis on the multi-hop transmissions, topology control and routing-level issues. Specifically, the paper considers energy efficient information broadcasting in WSNs deploying co-operating nodes which by adjusting their transmission ranges minimize the total transmitted power in the network. To this end, the design of routing protocols with a single relay is proposed for multiple multicast sessions in a network with randomly distributed nodes. The protocols take advantage of topological diversity created by adapting the transmission power and exploit the benefits of network coding in a system where nodes are periodically generating data packets. Energy efficiency of the conventional, store-and-forward, and network coding based relaying schemes is analyzed in different propagation conditions and for various node densities.

This paper is concerned with the computationally efficient selection of relays and assignment of transmit power values in wireless networks deploying cooperating nodes. The objective is to minimize the transmitted power required to exchange the data between two nodes. Specifically, the design of routing protocols with multiple store-and-forward relays along a data path is proposed for multiple unicast sessions in a network with randomly distributed nodes. The protocols are based on the knowledge of interdistances between nodes and, by adapting the transmission power, they control the topology to achieve the minimized total energy in networks with mesh type connectivity. In addition, the benefits of network coding are exploited for underlying networks with dynamic power allocations. Geometric ideas and abstractions are used to demonstrate that nodes which are closest to equi-spaced points distributed along the line of communication between a source and destination pair are the most energy efficient choices for relays. An analysis of the energy efficiency of the conventional store-and-forward and network coding based relaying schemes under different propagation conditions and for various node densities, with potential theoretical improvements corroborated through simulations, are also provided.

This paper is concerned with the power allocation problem in a transmit diversity wireless system with mean channel gain information. For a given set of mean channel gains between nodes, the aim is to find the power allocation and corresponding network topology that minimizes the total transmit power for nodes involved in the cooperative communications between the source and the destination, where all of the transmitters use single omnidirectional antennas. Specifically, the selection of store-and-forward relays deploying Alamouti-type distributed space-time coding along a multihop connection is proposed for a network with randomly distributed nodes and Rayleigh fading. By adapting the transmission power, the proposed data forwarding and processing schemes control the selection of relay nodes utilizing space time coding to minimize the total energy required to transmit the information. In addition to addressing the geometric analysis of the power-efficient topology problem, this paper also focuses on finding computationally efficient algorithms for the selection of relay nodes which will result in a topology formation requiring close to minimum energy.

This paper investigates the user and channel diversity in OFDMA wireless systems with network coding. In particular, the paper introduces an adaptive resource allocation scheme to minimize the total transmit power while maintaining a required end-to-end BER. The proposed adaptive sub-carrier allocation scheme de-couples the bit loading of the network coded OFDMA system into three independent bit loadings on three OFDM links. This approach allows the deployment of a conventional bit loading algorithm for OFDM on individual links. The simulation results show that, in frequency selective Rayleigh fading channels, the proposed low-complexity resource allocation scheme can significantly reduce the total power consumption in the network and maintain a targeted BER.

Unequal error protection (UEP) for multimedia communications relies on transmitting more important data through the sub-channels experiencing lower bit error rates (BERs). In radio broadcasting, UEP is implemented by deploying multiresolution (MR) modulations which allow the support for users close to the transmitter with higher perceived recovered image quality, while the users farther away experience the acceptable quality. This paper proposes a new approach to design MR modulations for such an image broadcasting scenario that optimizes the near users quality by exploiting the inherent scalability in image compression and UEP flexibility in 2-D modulation schemes. The proposed new framework for the design of MR modulations effectively integrates constellation distances and priority bits assignments, resulting in two user optimized joint source-channel coding. We present the simulation results for near and far users's image quality in such two-tier optimized radio broadcasting systems.

Errors in data measurements for network tomography may cause misleading estimations. This paper presents a novel technique to model these errors by using sparse code shrinkage (SCS) method. SCS is used in the field of image recognition for denoising the image data and we are the first to apply this technique for estimating error free link delays from erroneous link delay data. To make SCS adoptable in network tomography, we have made some changes in the SCS technique such as the use of Non Negative Matrix Factorization (NNMF) instead of independent component analysis (ICA) for the purpose of estimating sparsifying transformation. The estimated (denoised) link delays are compared with the original (error free) link delays based on the data obtained from a laboratory test bed. The simulation results verify the accuracy of the proposed technique.

This paper presents space-time block codes (STBC) constructed by the orthogonalization of Walsh-Hadamard transform domain coefficients. The novel Walsh-Hadamard STBC (WHSTBC) provides full rate and full diversity order when the number of receive antennas is at least equal to the number of transmit antennas, with appropriate pre-coding of the PSK or QAM modulated symbols. Hadamard matrices exist for orders equal to N = 2n, where n ≥ 1 and lead to square WHSTBCs with minimal delay. The structure of WHSTBCs allow for simple decoupling and decoding. Simulation results and performance analysis are presented for N × N matrices with N = 2, 4, and 8.

This paper introduces a novel peak-to-average power ratio (PAPR) reduction method in orthogonal frequency division multiplexing (OFDM) systems by deploying wavelet packet pre-processing of the quadrature amplitude modulation (QAM) symbols. Specifically, joint inverse discrete wavelet packet and Fourier transformations (IDWPT and IDFT) of QAM symbols are calculated at the transmitter with the purpose of minimizing the PAPR of the OFDM frame to be transmitted. The wavelet packet tree representing a reversible IDWPT chosen at the transmitter is communicated to the receiver as side information, where the output of the DFT block is passed through the DWPT to recover the QAM symbols. As the DWPT is a orthonormal transformation, the proposed method preserves the average transmitted energy while maintaining the integrity of the transmitted information. With a small level of redundancy for side information, the proposed scheme achieves 5.5 dB reduction in PAPR over the traditional OFDM system as measured using the complementary cumulative distribution function (CCDF) of the OFDM signals at the clipping probability of 10-4.

An increasing number of real-time applications in packet networks uses erasure codes to cope with packet losses. Most of these codes were designed originally for bit or symbol oriented transmission. This paper introduces packet oriented block codes for the recovery of lost packets. Specifically, a family of systematic erasure codes is proposed based on the Vandermonde matrix applied to a group of k information packets to construct r redundant packets. The elements of the Vandermonde matrix are bit level right arithmetic shift operators applied to the information packets. With low-overhead packet padding, the code design is applicable to packets of any size with the same lengths within the block of k information packets. The recovery of lost packets is based on inverting a matrix corresponding to the coefficient -Vandermonde- matrix augmented by the identity matrix with the rows removed according to the sequence number of the lost packets. The general code design principles are illustrated in this paper with examples of codes of different parameters. Erasure recovery capability of the proposed codes is characterized by simple decoding procedures. The code designs are tested using Monte Carlo simulations and their performance shows good agreement with theoretical results.

Due to layer interactions, packets in cross layer protocol designs are impaired with both errors and packet loss, where the latter is also referred to as a packet erasure. In real-time applications, packet-level forward error correction (FEC) schemes are favorable candidates to enhance the performance of such protocols without retransmission. This paper proposes to use one type of code to recover from both impairments. In particular, the approach builds on recently introduced packet oriented systematic block codes in which parity matrix depends on the Vandermonde structure with shift operators. These codes are maximum distance separable (MDS) and have the advantage over other MDS codes of simple encoding/decoding processes. At the packet level, de-coupling of erasure recovery and the error correction processes is a challenging task, and this paper explores the advantages of packet-level product of two codes: one for erasure recovery and the other for error correction. Monte Carlo simulations show that the throughput of the proposed system improves when applying both error correction and erasure recovery compared to a system applying erasure-only recovery with equivalent overall minimum distance.

This paper proposes a design of packet oriented systematic block codes based on the Vandermonde matrix applied to a group of k information packets to construct r redundant packets which are transmitted together with the original packets into the network. The investigated codes are capable of correcting a single erroneous packet in a group of n = k+r received packets, irrespective of the number of bits in error within this packet. The elements of the Vandermonde matrix are bit level right arithmetic shift operators and this, combined with low-overhead packet padding, enables simple endcoding/decoding procedures as compared to some of the more traditional packet-level error correction approaches. The latter, similar to the codes proposed in this paper, is applicable to packets of any size with the same lengths within the block of k information packets. The correction of erroneous packet is based on syndrome decoding that provides both the location of the packet in error and the locations of the bits in error within this packet. The general code design principles are illustrated in the paper with examples of codes of different rates but the same minimum distance of three. The design performance is tested using Monte Carlo simulations and shows good agreement with theoretical results.

This paper applies the level crossing rate (LCR) and average fade duration (AFD) analysis to characterize clipping noise in filtered OFDM signals. Because orthogonal frequency division multiplexing (OFDM) signals exhibit complex Gaussian process behavior, well established results for the Rayleigh enve- lope of the correlated Gaussian process are used to derive the LCR and AFD statistics of the OFDM signal at the output of a square-root raised cosine shaping filter. The LCR and AFD information is then used to determine the statistics of the OFDM signal that passes through a soft-limiter, approximating at the baseband high power amplifier (HPA) memory-less nonlinearity. Simulation results corroborate theoretical derivations for the LCR and AFD statistics in real OFDM signals. The results obtained are important in predicting the clipping noise impact on the in-band and adjacent channel interference.

This paper develops a new method for peak-to- average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems using an expanded constellation of points in quadrature amplitude modulation (QAM). On each OFDM subcarrier, the scheme uses a specialized representation of QAM symbols that allows mapping of a group of symbols from the conventional constellation onto an alternative symbol from the external square of signalling points. The design of the expanded constellation maintains the minimum distance between signalling points with a minimal increase in the average power. Its advantage stems from the location of the alternative signalling point being "radially symmetric" to the group of original signalling points in QAM. In systems using coding, the alternative signalling points represent recoverable erasures introduced at the transmitter for the purpose of reducing PAPR. The proposed PAPR reduction method is especially applicable to QAM schemes with high number of constellation points such as M = 64 and M = 256. Significant PAPR reduction is achieved by careful mapping and selection of alternative signalling points for transmission that result in lower PAPRs. Specifically, the complementary cumulative distribution function (CCDF) of the modified OFDM signal shows (5) dB improvement in PAPR at a clipping probability of 10-4over the original OFDM signal.

This paper proposes a new method for peak to average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems using two alternative signalling points to represent one symbol. In this redundant signal representation with no need for side information, the expanded constellation of signalling points used on each OFDM subcarrier is comprised of a conventional modulation scheme such as PSK or QAM and an external circle of alternative signalling points. The design of the expanded constellation maintains the minimum distance between signalling points and its advantage stems from the location of the alternative signalling point being radially symmetric to the original signalling point in the conventional constellation. Significant PAPR reduction is achieved by choosing for transmission signalling points which result in lower PAPRs. Specifically, the complementary cumulative distribution function (CCDF) of the modified OFDM signal shows about a five (5) dB improvement in PAPR at clipping probability of 10 4 over the original OFDM signal. This performance is comparable to that in similar PAPR reduction schemes; however it is achieved at a significantly lower computational overhead.

A new multi-node pruning algorithm is presented to overcome high peak-to-average power ratio (PAPR) of transmitted signals in multicarrier modulation systems such as orthogonal frequency division multiplexing (OFDM) and wavelet packet modulation (WPM). Specifically, a wavelet packet tree pruning technique with multiple node and multiple pass processing is proposed for the reduction of PAPR in WPM systems. Multiple tree structures are generated for the modulation of a given data input, and the output of tree with the smallest PAPR is selected for transmission. A full wavelet packet tree is dynamically pruned via joining of multiple non-leaf or non-terminal nodes to achieve a minimized PAPR. The information about the pruned tree is sent as side information similar to techniques such as selective mapping (SLM) in OFDM systems. Using a small level of redundancy for side information, the proposed scheme achieves significant reduction in PAPR at the expense of acceptable computational complexity. The complementary cumulative distribution function (CCDF) of the PAPR optimized signal shows about a 5 dB improvement over the original WPM signal.

When successive interference cancellation (SIC) is employed, the mobile users with high signal-to-interference-plus-noise ratio (SINR) do not necessarily produce excessive multiple access interference as they do when single user detection is employed. Thus, in cellular CDMA systems employing SIC, there exists an alternative receiving power pattern other than the geometric receiving power pattern, which can significantly reduce the average outage probability of the systems.

This paper introduces a peak-to-average power ratio(PAPR) reduction methodology in orthogonal frequency division multiplexing (OFDM) systems by deploying pilot tones in PAPR optimized configurations. Conventionally, the pilot tones in OFDM are used for channel estimation and carrier tracking. In this paper, in addition to maintaining their conventional functions, pilot tones, i.e., their signaling points and positions, are carefully chosen to "balance" the envelope peaks in the OFDM frame. Specifically, two methods are proposed, where both the magnitude and the phase information of the pilot tones are modified to reduce the PAPR of the OFDM signal. In the first method, similar to conventional applications, the pilot tones occur at the deterministic, known to the receiver, subcarriers whereas in the second method, a relaxation in the position of pilot tones is allowed. The proposed schemes achieve significant reduction in the PAPR, as measured using the complementary cumulative distribution function (CCDF) of the OFDM signal, without affecting the data rate of the system.

High peak-to-average power ratio (PAPR) of transmitted signals is a major drawback for multicarrier modulation systems such as orthogonal frequency division multiplexing (OFDM) and wavelet packet modulation (WPM). In this paper, wavelet packet tree pruning is proposed for the reduction of PAPR in WPM systems. In this technique, a full wavelet packet tree is dynamically pruned via joining and splitting of terminal nodes to achieve a minimized PAPR. Specifically, alternative mappings of data symbols onto different tree structures are generated, and the time domain sequence with the smallest PAPR is transmitted. The information about the pruned tree is sent as side information similar to techniques such as selective mapping (SLM) in OFDM systems. Using a small level of redundancy for side information, the proposed scheme achieves significant reduction in PAPR at the expense of acceptable computational complexity. The complementary cumulative distribution function (CCDF) of the PAPR optimized signal shows about a 3.5 dB improvement over the original WPM signal.

Analytical expressions that allow one to analyze the total transmitted power in various cellular systems are important design tools in network optimization. This paper develops a new method of finding the total transmitted power by mobile stations (MSs) in systems with different power profiles and very general propagation conditions. Specifically, a closed-form expression is derived, based on the assumption that MSs are distributed within the cell according to a two-dimensional (2-D) Poisson point process and the observation that user distances to the base station (BS) form a gamma distribution. By using this model, the total power is derived by finding the fractional moment of the gamma distribution. A simulation model developed verifies the correctness of the theoretical derivations, with the users distributed randomly in a plane. Various propagation constants are considered. Close agreement is found between the calculated and simulated transmitted powers.

This paper proposes a new method for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems using forward error correction (FEC). The scheme combines the intentional insertion of correctable errors into the data stream with a specialized bit mapping. The latter deviates from traditional Gray encoding of bits into modulation symbols in order to maximize the benefits of FEC-based PAPR reduction. Using the code redundancy, the proposed scheme achieves significant reduction in PAPR and satisfactory bit error rate (BER) performance at the expense of acceptable computational complexity. Specifically, the complementary cumulative distribution function (CCDF) of the coded signal shows about a 5dB improvement over the original OFDM signal. In addition, BER performance in an additive white Gaussian noise demonstrates trade-offs between reduction in PAPR and remaining error correction capability of the deployed codes.

In this paper, the effects of imperfect power control on the reverse link outage probabilities of cellular CDMA systems employing successive interference cancellations (SIC) are thoroughly investigated. Both theoretical and computer simulation results show that the capacity of cellular CDMA systems employing SIC are very sensitive to imperfect power control. Hence, this is a large capacity gap between the systems following current power control standards and those with perfect power control. By tightening power control standards with new technologies, the capacity of cellular CDMA system employing SIC can be improved significantly.

This paper extends the analysis of a statistical methodology for source detection and localization (SDL) in a network of randomly distributed wireless nodes equipped with homogeneous and omni-directional sensors. The investigations are focused on SDL with respect to the nearest sensor node and are based on the observed source (phenomenon) energy. In this framework, the SDL algorithms are viewed as classification problems which are solved using pattern recognition techniques. In the presented approach: (i) sensors are randomly distributed and little is known about their exact locations; and (ii) a self-calibrating mechanism is proposed for creating the dataset whose feature vectors constitute the reference points for sensor locations in the space of sensor readings. The performance of the proposed algorithms is evaluated through Monte Carlo simulations and is demonstrated to be robust in the presence of noise and changes in the propagation environments.

Product codes are powerful codes that can be used to correct errors and/or recover erasures. The focus of this paper is to evaluate the performance of such codes under the erasure scenarios. Judging the erasure recovery performance of a product code based on its minimum distance is pessimistic because the code is actually capable of recovering many erasure patterns beyond those with the number of erasures determined by the minimum distance. By investigating the non-correctable erasure patterns, this paper develops a tight upper bound on the post-decoding erasure rate for any binary product code. The analytical derivations are verified through computer simulations using Hamming and single parity check (SPC) product codes. A good agreement between the derived formulas and simulation results is documented

This paper presents a differential space-time transceiver over multiple-input multiple-output (MIMO) time-dispersive channels. The underlying idea is to transform the block Toeplitz received signal structure caused by the finite impulse response (FIR) multipath channels into a block circulant matrix structure by deploying specialized signaling when transmitting through multiple antennas. This structure is then exploited by using the efficient space-time (ST) processing at the receiver for the mitigation of the channel multipath effects. The new, low complexity, transceiver is based on cyclic group codes and a differential ST demodulation. The proposed scheme falls into the category of the deterministic approaches that are able to operate on short sample data and do not face convergence problems. Simulation results verify the robust performance of the scheme over the MIMO-FIR fading channels.

The OFDM modulation scheme is characterized by the Gaussian-like signal behavior with a relatively high peak-to-average power ratio (PAPR). As a result, it is very sensitive to nonlinear distortions, which arise mainly from the high power amplifier (HPA). This paper proposes an algebraic solution to compensate at the transmitter for nonlinearity of the HPA with memory effects, where the HPA behavioral model is represented by the Hammerstein structure, a cascade of a memoryless nonlinear block followed by a linear filter. In particular, a frequency domain parameter identification methodology is developed that first estimates the parameters of the unknown nonlinearity, which is modelled through a polynomial expansion. The frequency response of the unknown filter is then calculated, in order to capture the memory effects in the system. Using the identified nonlinear system parameters, an inverse Wiener structure, consisting of a cascade of the inverse filter and the inverse memoryless nonlinearity, is constructed preceding the HPA, in order to predistort the input signals so as to achieve overall linear transmitter characteristics.

The paper extends the analysis of a novel data link layer mechanism introduced in our previous work for real-time service provisioning in multi-hop wireless networks. To combat packet loss along unreliable paths connecting the source with the destination, (i) packet transmissions are distributed along the multiple paths connecting joint nodes and (ii) the redundancy packets are utilized to recover the lost packets on these intermediate connections. The regenerating nodes (RNs), where the actual packet loss recovery is performed in the network, minimize the accumulated number of lost packets at the destination. This joint application of packet level forward error control (FEC) and multiple path routing allows the requirements of real-time transmissions, such as fixed delays and guaranteed packet loss rate (PLR), to be met. The proposed scheme achieves load balancing along the multiple paths which are chosen for packet forwarding based on their PLR. The scheme is sufficiently flexible to accommodate various constraints for delay and reliability that can be tailored to the specific applications. Monte Carlo simulations demonstrate the robust performance of the proposed scheme in different topology and PLR scenarios, with special attention given to the choice of the RN positions in the network.

This paper proposes a new framework in mobile ad hoc networks (MANET) for reliable multipath routing with fixed delays based on packet level forward error control (FEC). The novelty of this work stems from the integrated optimization of the redundancy at the path and the FEC packet levels to arrive at the concept of the regenerating nodes. The regenerating nodes can reduce the packet loss rate (PLR) between the source and the intermediate nodes so that, eventually, the PLR between the source and the destination is minimized. In general, the residual PLR in the system is reduced to the PLR on the connection between the last regenerating node and the destination. Extensive Monte Carlo simulations are provided to demonstrate the robust performance of the proposed scheme in the network environments with frequently changing topologies and PLR scenarios. The scheme accommodates various constraints for delay and reliability in terms of PLR that can be tailored to the specific applications, such as real-time multimedia services in MANET.

This paper presents a space-time multiple-input and multiple-output (MIMO) transceiver for reliable transmissions over frequency selective fading channels using conventional single-carrier M-ary PSK or QAM modulations. The novelty of the proposed scheme is in efficient exploiting the induced circulant structure of the new signaling in the context of MIMO setup so that the intersymbol interference (ISI) effects could be fully mitigated at the receiver using algebraic solutions. It is demonstrated through Monte-Carlo simulations that the performance of this scheme over time-dispersive channels is comparable to that of MIMO-OFDM. OFDM has high peak to average power ratio (PAPR) and demands the use of highly linear power amplifiers (PA). The proposed scheme offers the advantage of reduced constraints on the PA linearity, which is critical in wireless applications.

This paper describes a novel forward error correction (FEC) based technique, VHPG FEC, which combats packet losses and packet errors simultaneously. The scheme proposed uses a two-dimensional (2-D) coding approach in which, at the encoder, information carrying packets are arranged vertically to form the 2-D matrix. The first code is applied along the horizontal direction to form the redundancy packets mainly to recover from lost packets; the second code is applied along the vertical direction within the individual packets to minimize the bit error rate (BER). Within the group of packets, the overall effect of this scheme is the reduction in the effective packet loss and the BER without need for retransmission. The scheme is applicable in environments where the packet loss is not exclusively a result of high BER and where the transmission time constraints are critical. The adaptive extension of the scheme proposed, AVHPG FEC, is introduced to deal with dynamic wireless channel characteristics. The performance of the VHPG coding is analyzed through theoretical calculations to illustrate the choice of coding parameters for various channels.

A texture model for synthetic aperture radar (SAR) images is presented. Specifically, a sea surface in satellite images is modeled using the two-dimensional (2-D) fractionally integrated autoregressive-moving average (FARIMA) process with a non-Gaussian white driving sequence. The FARIMA process is an ARMA type model which is asymptotically self-similar. It captures the long-range as well as short-range spatial dependence structure of an image with a small number of parameters. To estimate these parameters, an efficient estimation procedure based on a spectral fit is presented. Real-life ocean surveillance radar images collected by the RADARSAT sensor are used to evaluate the practicality of this FARIMA approach. Using the radial power spectral density, the new model is shown to provide a more accurate description of the SAR images than the conventional moving-average (MA), autoregressive (AR), and fractionally differenced (FD) models.

This paper presents a data traffic model capable of describing the long-range as well as short-range dependence structure of packet data traffic. Specifically, we use the fractionally integrated autoregressive-moving average (FARIMA) process with non-Gaussian white driving sequence to describe packet arrival rate in a unit time. We introduce a procedure to estimate the fractional differencing parameter and ARMA coefficients: this procedure uses a cepstrum approach and does not require any prior knowledge about the driving noise distribution and the type of ARMA system. Since the main purpose of workload modeling is to aid in network performance evaluations, we are particularly interested in using the FARIMA model to predict bandwidth requirements for network traffic. We propose a dynamic bandwidth allocation strategy by employing linear predictors designed based on the estimated FARIMA parameters.

We consider the performance of frequency-hopping spread spectrum (FH SS) radio networks in a Poisson field of interfering terminals using the same modulation and power. The problem is relevant to wireless random-access communication systems where little information about transmitters requires stochastic modeling of their positions. Assuming that the signal strength is attenuated over distance r on average as 1/r/sup m/, we show that the interference in the network could be modeled as a mixture of Gaussian and /spl alpha/-stable noise. Based on this modeling, we derive expressions for the probability of error (P/sub e/) for systems with M-ary frequency shift keying (FSK) which use conventional envelope detectors. Because conventional envelope detectors are optimum only in Gaussian noise and are suboptimum in the noise considered, we also investigate noncoherent detectors which offer improved performance. We examine receivers with limiting nonlinearities and detectors which are optimal in Cauchy noise. Numerical calculations and Monte Carlo simulations are provided to confirm the accuracy of the analysis presented. The results obtained are useful in the performance evaluation of multiple-access radio networks in environments varying from urban settings to office buildings with deterministic and stochastic propagation laws such as lognormal shadowing and Rayleigh fading.

We present a new, suboptimum, method for the detection of signals in noise for which standard methods of inference are difficult to implement. The method is based on the empirical characteristic function (ECF) and exploits the correlation structure of the ECF evaluated at the finite number of points. We assume discrete time detection so that N i.i.d. data samples are available per symbol. We examine the performance of the proposed method for the mixture of /spl alpha/-stable and Gaussian noise. The detectors based on the ecf show substantial improvements in performance compared to linear detectors and exhibit better performance than the locally optimum (LO) detectors.

This paper considers the performance of FH SS radio networks in a Poisson field of interfering terminals using the same modulation and power. Assuming 1/r/sup m/ attenuation of signal strength over distance, the interference in the network is modeled as a mixture of Gaussian and circularly symmetric /spl alpha/-stable noise. The problem is relevant to mobile communication systems where the mobility of users requires random modeling of transmitter positions in the network. We derive formulas for the probability distributions of the interference in FH SS radio networks. We generalize the results of Sousa (see IEEE Trans. I.T., vol.38, no.6, p.1743-1754, 1992) where attention was limited to Cauchy random variables, a special subclass of stable distributions, and where the effect of a background (Gaussian) noise was neglected. Based on the formulas derived, we calculate the probability of symbol error for radio links in environments varying from urban settings to office buildings. The results obtained allow the prediction of the performance of wireless systems under a wide range of conditions.

We consider the performance of frequency-hopping spread spectrum (FH SS) radio networks in a Poisson field of interfering terminals using the same modulation and power. The problem is relevant to mobile communication systems where the mobility of users requires random modeling of transmitter positions in the network. Assuming logarithmic attenuation of the signal strength over distance between the transmitter and receiver, we show that the interference in the network could be modeled as a mixture of Gaussian and circularly symmetric /spl alpha/-stable noise. Based on this model, we derive union bound approximations for the probability of error for FH systems with M-ary frequency shift keying (FSK). We generalize some of the results of Sousa (see IEEE Trans. I.T., vol.38, no.6, p.1743, 1992), where the focus was limited to Cauchy random variables (RVs), a special subclass of stable distributions, and where the effect of a background (Gaussian) noise was neglected. Numerical calculations and Monte Carlo simulations confirm the accuracy of our analysis. The results obtained allow the prediction of wireless system performance in environments varying from urban settings to office buildings.

The impact of nonGaussian impulsive noise combined with Gaussian noise on the performance of the binary transmission is analyzed. The impulsive noise is modeled as an alpha-stable process. The probability of error for optimum, linear and nonlinear receivers is derived. The proposed nonlinear detectors show substantial improvements in performance compared to linear ones. The obtained results will be useful in performance evaluation of digital communication links subject to Gaussian and impulsive noises.>