Efficient message authentication is crucial for secure communications. However, the traditional integrity check scheme imposes significant overhead by appending a unique Message Authentication Code (MAC) to each message. At the same time, existing solutions such as aggregate and compound MACs attempt to reduce this overhead by transmitting one MAC tag per multiple messages. This strategy is ineffective in lossy environments where any message loss prevents the corresponding tag from verifying the other messages assigned to it. In this paper, we introduce a novel two-dimensional (2D) MAC structure that organizes messages in a 2D format and computes a single authentication tag for each row and column. This approach enables precise identification of modified or erroneous messages using fewer tags than conventional methods. By integrating the 2D MAC structure with superimposed coding techniques, we further reduce bandwidth consumption by allowing simultaneous transmission of messages and authentication tags. Experimental validation in Wi-Fi networks demonstrates over 20 % increase in authentication throughput, with analytical results indicating additional improvements when tags are superimposed onto the message.

We propose a novel stealthy message authentication technique designed to completely obscure the existence of the digital signature, rendering it secure against integrity attacks. This innovative approach not only prevents digital signature forgery but also evades detection by potential attackers, proactively safeguarding the authentication scheme. The core idea involves superimposing the digital signature onto the message and harnessing the capabilities of multiple input multiple output (MIMO) techniques to obfuscate the signature. We demonstrate that the total detection error probability (sum of false alarm and miss detection probability) of the signature approaches unity with an increasing number of transmitter antennas, indicating the undetectability of the signature, regardless of its transmission power. Furthermore, we analyze the impact of this covert verification on the signature decoding error probability.

We propose a novel covert message authentication technique designed to completely obscure the existence of the digital signature, rendering it secure against integrity attacks. This innovative approach not only thwarts counterfeiting attempts of digital signatures but also effectively evades the scrutiny of potential hackers, thereby protecting the authentication scheme proactively. The core idea involves superimposing the digital signature onto the message and harnessing the capabilities of multiple input multiple output (MIMO) techniques to obfuscate the signature. We demonstrate that the total detection error probability (sum of false alarm and miss detection probability) of the signature approaches unity with an increasing number of transmitter antennas, indicating the undetectability of the signature, regardless of its transmission power. Furthermore, we analyze the impact of this covert verification on the signature decoding error probability and the authenticated message throughput, providing insights into the overall effectiveness of the proposed technique in protecting the authenticity of the message. We also investigate how artificial noise affects the total detection error probability and the authenticated message throughput. Finally, we compare two approaches to signature protection: signature secrecy which prevents eavesdroppers from gaining any meaningful information about the signature and signature covertness which hides the signature transmission.

This paper pioneers the exploitation of power domain superposition to embed covert messages within overt ones in a two-user uplink Non-Orthogonal Multiple Access (NOMA) system. This eliminates the need for a dedicated covert trans-mitter, enhancing practicality. Our method thwarts conventional radiometer detection at Willie, necessitating Likelihood Ratio Testing (LRT), which we evaluate under optimized overt transmission rates and imperfect Successive Interference Cancellation (SIC) scenarios at Willie. We then minimize Willie's detection error probability by optimizing his detection thresholds and subsequently maximize his minimum DEP by exploiting the user's transmit power and overt-covert power allocation. We show that covert communication is safe if the warden, Willie, doesn't decode any overt message and converges to 1 under high transmission power at users.

Healthcare sensor authentication can be challenging due to the limited energy capacity and small size of the devices. The need for additional hardware, such as NFC or displays, for secure pairing, as imposed by the Bluetooth Low Energy (BLE) standard, further worsens this challenge. One promising alternative for node authentication is the use of Radio Frequency Fingerprint Identification (RFFI). We investigate RFFI’s effectiveness within Wireless Body Area Networks (WBANs) using the real-world BLE-WBAN dataset, which includes signals emitted by body-mounted BLE sensors inside an anechoic chamber. Diverging from most prior research, our approach leverages higher fidelity input (real and imaginary parts together) in Complex-Valued Neural Networks (CV-NNs), despite their increased computational cost, to realize a substantial improvement in fingerprinting accuracy over traditional Real-Valued Neural Networks (RV-NN). Our experiments demonstrate that CV-NNs excel, particularly at higher sampling rates, and reveal that the human body can positively influence RFFI, achieving up to 88% accuracy in on-body node fingerprinting among 12 nodes. While our results are promising, they highlight the need for further validation to confirm CV-NNs’ potential to bolster RFFI in WBANs.

The lack of availability of real-world RF datasets has often impeded physical layer research relating to IoT and Health IoT sectors. Towards this end, this paper presents an unprecedented open-source Bluetooth Low Energy (BLE) dataset, encompassing 100 MSps radio signal recordings from 13 ESP32 IoT nodes in both on-body and over-the-air settings within an anechoic chamber, utilizing the dual receiver setup on USRP x310. Wideband (complete 2.4 GHz ISM band) acquisition and high sampling frequency ensure exceptional resolution and room for use case-specific sampling scalability in the dataset. We delineate the dataset's acquisition methodology, spotlight its inherent advantages, and offer a valuable Python tool to process and scrutinize the raw IQ samples. To facilitate the use of datasets in machine learning applications for the physical layer, we have incorporated this tool within a dataset hosted on a public GitHub repository. Here, we explore preliminary feature selection and conduct tests and training of machine learning models, including Random Forest and K-Nearest Neighbors (KNN) that achieve 81% accuracy in node classification for static on-body frames. This demonstrates the dataset's versatility in various scenarios, such as authentication and localization.

We explore leveraging the multiplicity of overt (public) messages, destined for different receivers through different channels, for hiding the transmission of a covert (private) message. The transmitter hides the covert message against a warden by superimposing it onto an overt message. We determine the optimum rule for choosing the overt message to maximize the total detection error probability (sum of the probability of false alarm and missed detection) at the warden. In addition, the channel variation is exploited to minimize the throughput loss on the overt message caused by the superimposition of the covert message. We show that the maximum total detection error probability converges fast to 1 as the number of overt messages (channels) increases; the total detection error probability is independent of the transmission power; and that a positive covert rate (bits per channel use) can be achieved while keeping the total detection error probability arbitrarily close to 1. These findings indicate that the multiplicity of overt messages (channels) and channel variations can be exploited to achieve a positive covert rate.

Cryptography has been used as the first line of defense to ensure data integrity. However, it incurs a significant overhead for short packets which represent the most common form of traffic in emerging applications, such as the Internet of Things. In this paper, we propose an interdisciplinary framework for detecting false data in short packets that are collected from multiple sources through a relay. The proposed scheme performs a lightweight cryptographic integrity check that employs a short message authentication code, thereby reducing the overhead for data integrity, followed by the maximum a posteriori (MAP) test at the physical layer that detects any remaining false data that the cryptographic integrity check misses. This interdisciplinary approach interplays between the cryptographic integrity check and the physical-layer integrity check to assure the data integrity of short packets with reduced overhead and low latency. The proposed scheme can also provide a significant reduction in the average probability of detection error over the traditional cryptographic integrity check.

We present a covert (low probability of detection) communication scheme that exploits the node multiplicity and channel variations in wireless broadcast networks. The transmitter hides the covert (private) message by superimposing it onto a non-covert (public) message such that the total transmission power remains the same whether or not the covert message is transmitted. It makes the detection of the covert message impossible unless the non-covert message is decoded. We exploit the multiplicity of non-covert messages (users) to provide a degree of freedom in choosing the non-covert message such that the total detection error probability (sum of the probability of false alarm and missed detection) is maximized. We also exploit the channel variation to minimize the throughput loss on the non-covert message by sending the covert message only when the transmission rate of the non-covert message is low. We show that the total detection error probability converges fast to 1 as the number of non-covert users increases and that the total detection error probability increases as the transmit power increases, without requiring a pre-shared secret among the nodes.

We consider hiding a covert (private) message in non-orthogonal multiple access (NOMA) systems by superimposing (embedding) it under non-covert (public) messages. We determine the total detection error probability (sum of false alarm and missed detection probability), the adversary's optimum detection strategy that minimizes the total detection error probability, and the communicator's optimum message hiding strategy that maximizes the total detection error probability. Additionally, we explore exploiting the channel variations to further increase the total detection error probability. We show that the total detection error probability increases and converges to 1 as the number of users increases and that the total detection error probability can be increased by increasing the transmission power when the channel variation is exploited.

We present the physical-layer maximum a posteriori (MAP) test for detecting false data in multiple-source wireless relay networks. The MAP test, which minimizes the average probability of detection error, exploits the noisy (erroneous) information about the true packet that the destination receives (overhears) directly from the source nodes as a reference. We show that the average probability of detection error decreases exponentially as the number of source nodes increases, regardless of the reliability of the reference information. This indicates that the multiplicity of source nodes can be leveraged to construct a powerful integrity check mechanism for detecting false data at the destination. We also present a parallel MAP test that improves the detection accuracy when the number of source nodes is limited and overhearing channel disparities are high. Then, we present a packet recovery mechanism to recover false alarmed packets, i.e. unmodified packets that are mistakenly declared as modified, by the MAP test and thereby to improve the throughput.

Covert or low probability of detection communication is crucial to protect user privacy and provide a strong security. We analyze the joint impact of imperfect knowledge of the channel gain (channel uncertainty) and noise power (noise uncertainty) on the average probability of detection error at the eavesdropper and the covert throughput in Rayleigh fading channel. We characterize the covert throughput gain provided by the channel uncertainty as well as the covert throughput loss caused by the channel fading as a function of the noise uncertainty. Our result shows that the channel fading is essential to hiding the signal transmission, particularly when the noise uncertainty is below a threshold and/or the receive SNR is above a threshold. The impact of the channel uncertainty on the average probability of detection error and covert throughput is more significant when the noise uncertainty is larger.

We study multi-base station (BS) preamble detection schemes for the narrow-band Internet of Things (NB-IoT) random access by using stochastic geometry analysis. Specifically, we compare the preamble detection performance of two baseline detection schemes: Quantize-and-Forward (QnF) and Detect-and-Forward (DnF). QnF requires the feedback of quantized received power levels while DnF requires 1-bit feedback of local detection result. Our results show that DnF scheme outperforms QnF scheme when the backhaul capacity is limited or when the minimum distance between user and BSs is less than a threshold. Our results also show that the use of multiple collaborative BSs can lead to a significant improvement of the preamble detection performance, as well as reduction of the total power of the preamble transmission.

This paper proposes a new simultaneous spectrum sensing (SS) and energy harvesting (EH) scheme, called integrated SS-EH, where all of the incoming radio-frequency (RF) power is used for EH. Then, SS is performed based on a fraction of the harvested power. The proposed approach does not require a separate energy detector, which needs a power-hungry radio front end. Therefore, the energy consumption and hardware complexity for SS can be reduced significantly. Furthermore, it can increase the harvested energy over the conventional separated SS-EH scheme, where SS and EH are performed separately, and thus, only a fraction of the incoming RF power can be used for EH. The combined benefit of reduced energy consumption for SS and increased energy harvest allows more energy to be available for communication, which results in an increase of the throughput. The probability of false alarm and missed detection, the average harvested energy, and the average throughput are analyzed in Rayleigh fading channel and compared with the conventional separated SS-EH scheme. A mixed SS and EH scheme is proposed in cooperative SS and EH environment where each sensor operates in either the integrated SS-EH or the separated SS-EH mode to improve the sensing accuracy at the fusion center.

This paper investigates a multi-band harvesting (EH) schemes under cognitive radio interweave framework. All secondary users are considered as EH nodes that are allowed to harvest energy from multiple bands of Radio Frequency (RF) sources. A win-win framework is proposed, where SUs can sense the spectrum to determine whether the spectrum is busy, and hence they may harvest from RF energy, or if it is idle, and hence they can use it for transmission. Only a subset of the SUs can sense in order to reduce sensing energy, and then machine learning is used to characterize areas of harvesting and spectrum usage. We formulate an optimization problem that jointly optimize number of sensing samples and sensing threshold in order to minimize the sensing time and hence maximize the amount of energy harvested. A near optimal solution is proposed using Geometric Programming (GP) to optimally solve the problem in a time-slotted period. Finally, an energy efficient approach based on multi-class Support Vector Machine (SVM) is proposed by involving only training SUs instead of all SUs.

This paper proposes an integrated spectrum sensing (SS) and energy harvesting (EH) scheme, where all of the incoming radio frequency (RF) power are used for EH. Then, SS is performed based on the harvested energy. This approach does not require a separate energy detector which needs power- hungry RF front ends. As a result, the energy consumption for spectrum sensing can be reduced significantly. Additionally, it can increase the harvested energy over the conventional separated SS-EH scheme which allows only a fraction of RF power to be used for EH. The probability of false alarm and missed detection are derived in Rayleigh fading channels and are compared with the conventional separated SS-EH scheme.

We propose a physical-layer technique for checking the integrity of information provided by an intermediate node (relay) in cooperative relay communication systems. The proposed approach, built on the theory of likelihood ratio test, exploits the physical-layer signal from the source in detecting any data modification (false data injection attack) made by the relay. We present the optimum detection method that minimizes the end-to-end outage probability and the minmax detection method that minimizes the maximum possible outage probability under unknown attack probability. We show that the optimum detection technique can provide almost the same end-to-end outage probability that can be provided by the ideal cryptographic technique that perfectly detects the false injection at the expense of high computational cost and bandwidth overhead. The proposed physical integrity check can be used as an additional layer of protection or can complement to the conventional cryptographic techniques.

We consider a multiple access relay network where multiple sources send independent data to a single destination through multiple relays, which may inject falsified data into the network. To detect the malicious relays and discard (erase) data from them, tracing bits are embedded in the information data at each source node. In addition, parity bits are added to correct the errors caused by fading and noise. When the total amount of redundancy, tracing bits plus parity bits, is fixed, an increase in parity bits to increase the reliability requires a decrease in tracing bits, which leads to a less accurate detection of malicious behavior of relays, and vice versa. We investigate the tradeoff between the tracing bits and the parity bits in minimizing the probability of decoding error and maximizing the throughput in multisource, multirelay networks under falsified data injection attacks. The energy and throughput gains provided by the optimal allocation of redundancy and the tradeoff between reliability and security are analyzed.

The advantage of cooperative communications often depends on the relay that can reliably receive a message from a source node, process it, and forward it to its intended destination node. In this paper, we consider the situation in which the relays cannot reliably decode the message due to a low signal strength or high interference. We propose a new cooperative relaying strategy that utilizes the information provided by unreliable relays to improve the reliability of decoding at the destination. The basic idea is to allow the relays to forward their decoder outputs as long as the destination can decode the message using the information provided by the source and all relays (called global information). The motivation is that even if each relay may not be able to decode the message based on its local information, the destination may still decode it using the global information. Only when the destination cannot decode the message, the relays discard their incorrect decoder outputs. We analyze the end-to-end outage probability of the proposed scheme as a function of the transmission rate, signal-to-noise ratio, and number of relays. We show that the proposed scheme can provide a significant improvement over the conventional schemes, particularly when the relays cannot reliably decode the message. If the SNR is high enough or the transmission rate is below a threshold, the proposed scheme can provide the same outage probability that can be provided by the genie-aided relaying that assumes perfect knowledge on the message by all relays.

We propose information alignment that enables the destination to mitigate jamming in wireless multi-source relay networks. A central idea is to make the message packets from the sources and those from the relay aligned in the same direction such that they can be canceled each other and only the forwarded decoding error caused by jamming remains at the destination. This enables the destination to determine the forwarded decoding error and to remove it from the received packet to restore the true codeword. We show that the proposed scheme can achieve the performance close to what can be achieved by the genie relay that completely knows the message packets and therefore always forwards the correct information.

We examine the effect of the field size on the probability of symbol error and the throughput in untrustworthy networks that employ random network coding, where the network nodes provide false data purposely or unknowingly and the information transmission is subject to channel error. We show that the probability of correct decoding decays exponentially with the number of combined packets and that the throughput scales as (log2q)/q bits per symbol transmission where q is the field size. We present the optimum field size that maximizes the throughput or minimizes the probability of symbol error in terms of the trustworthiness of node and the number of combined packets.

We consider random network coding in noisy large-scale multiple-access relay networks in which the source packets that are correctly received at a relay are linearly combined with randomly chosen coefficients and forwarded to the destination. We derive the union bound on the average probability of decoding error at the destination with the maximum likelihood decoding, averaged over all possible node locations and relay encoding rules. The union bound provides an upper bound to the probability of decoding error with the best network coding scheme and enables us to determine the error exponent. From the error exponent, we determine the reliability-rate tradeoff and the achievable rate at the high node density regime. The high node density analysis is useful for understanding the performance of large-scale multiple access relay networks. The energy saving at a source node offered by the energy expenditure at a relay node and the optimum constellation size that minimizes the energy per information bit (Eb/N0) are investigated as a function of reliability, rate, and node density. The effect of MIMO transmit modes at the relay nodes, when they are equipped with multiple antennas, on the network-wide reliability-rate tradeoff is investigated. The insight provided by the analysis is useful for understanding of the fundamental limit and tradeoffs in large-scale multiple-access relay networks with network coding.

We consider a multiple-access relay network where multiple source nodes send independent packets to a common destination with the assistance of multiple relay nodes. We assume that the relay nodes are equipped with multiple antennas and are allowed to choose either spatial multiplexing (SM) or transmit diversity (TD) in sending network coded packets. We verify the performance limit of conventional MIMO network coding and propose two optimization schemes to overcome this limit. To this end, we develop an integrated design methodology that jointly optimizes the redundancy offered by network coding at the relays and channel coding at the sources as well as the spatial redundancy offered by multiple antennas in order to minimize the end-to-end outage probability. We show that such joint optimization can provide a significant energy saving.

We examine the trustworthiness of random network coded information in untrustworthy networks, where the network nodes provide false data purposely or unknowingly and data transmissions are subject to channel errors. The trustworthiness of information x is defined as the probability of x being true. We show that the trustworthiness of random network coded packet decreases exponentially with the number of packets that are combined and that of random network coded symbol decreases monotonically with the field size. The latter indicates that the binary field is optimal in the sense of maximizing the trustworthiness of network coded symbol in untrustworthy networks. We analyze the fundamental tradeoff between the trustworthiness of coded packet and the information transmission rate in Rayleigh fading channel with additive white Gaussian noise.

We take a physical-layer approach in detecting the falsely injected packet (pollution attack) and removing it from the polluted packet to restore the true coded packet in wireless network coding system. The proposed scheme builds on the maximum likelihood detection principle which is optimal in the sense of minimizing the probability of detection error. It “recycles” the polluted packet by discarding only the faulty information and using the remaining part in recovering the message. This makes it unnecessary to retransmit new coded packets and allows uninterrupted communication even under the heavy attack. The proposed scheme can provide a significant improvement in the throughput and reliability over the cryptographic solutions without requiring any transmission overhead.

We consider a multiple access relay network where multiple source nodes send independent packets to a common destination with the assistance from a relay node. We assume that the relay node is equipped with multiple antennas and is allowed to choose either spatial multiplexing (SM) or beam forming mode as transmit diversity (TD). We develop an integrated design methodology for MIMO transmission, network coding at the relay node, and channel coding rate at the source nodes that minimizes the end-to-end outage probability.

We propose check-sum aided maximum a posteriori (MAP) approach in detecting the misbehaving relay that injects false data, drops valid data, and/or adds channel errors into the network encoder in noisy multiple access relay networks. The MAP detection is optimal in the sense of minimizing the probability of incorrect detection (false alarm and misdetection), while requiring no transmission overhead. The accuracy of misbehavior detection is improved by having a check node to overhear a set of source nodes and send a check-sum of overheard data to the detector. We derive the probability of false alarm and misdetection in Rayleigh fading noisy channels, and analyze the improvement of detection as a function of transmission overhead (rate) and signal-to-noise ratio.

We propose a physical layer approach to detect the relay node that injects false data or adds channel errors into the network encoder in multiple access relay networks. The misbehaving relay is detected by using the maximum a posteriori (MAP) detection rule which is optimal in the sense of minimizing the probability of incorrect decision (false alarm and miss detection). The proposed scheme does not require sending extra bits at the source, such as hash function or message authentication check bits, and hence there is no transmission overhead. The side information regarding the presence of forwarding misbehavior is exploited at the decoder to enhance the reliability of decoding. We derive the probability of false alarm and miss detection and the probability of bit error, taking into account the lossy nature of wireless links. We show that the proposed decoding with the aid of the MAP detection of misbehaving relay is within 1dB away from the genie-aided decoding.

We present a randomized cooperative broadcasting technique that is flexible to topology changes and robust to transmission errors in large-scale wireless networks. A single source sends a common message (codeword) to all nodes, and those nodes that decode the message correctly then generate a parity bit (a partial information on the message) and broadcast it to the remaining nodes. The remaining nodes integrate the original codeword from the source with the network-generated parity bits to construct a lower rate, and thus more powerful, error correcting code. The protocol overhead is significantly reduced by allowing each node to randomly generate a parity bit independent of other nodes. We show that the probability of decoding error decreases exponentially with the number of nodes in the network, and that the performance degradation relative to the deterministic parity generation (that requires a centralized coordination of nodes) becomes smaller as the number of nodes increases. We also show that the proposed approach enables all nodes to correctly receive the message within the first cooperation stage if the number of nodes is sufficiently large. Hence, the proposed approach is promising for applications in large-scale wireless broadcast networks.

We propose a cooperative concatenated coding scheme in multi-hop multiple access relay networks, where the parity bits generated in the previous hops are concatenated with those in the next hop such that the error recovery capability improves as the information travels through the network. It is based on the idea of cross-hop cooperation where the cooperation occurs across multiple hops, as opposed to the traditional cooperation within a hop. This approach enables the network coding gain to grow with each additional hop, which allows the relay nodes closer to the final destination to reduce their transmit powers. This feature is particularly useful in compensating the increased energy consumption from relaying more data as the data merge to the destination in multiple access relay networks. We derive the average probability of decoding error and throughput, averaged over all possible node locations, as a function of the number of hops taking into account the lossy nature of wireless links. We show how the relays should be traded across hops in order to maximize the end-to-end performance.

We present a new architecture for multi-antenna receivers that cancels the co-channel interference (CCI) using a single radio frequency (RF) and baseband (BB) chain, while still achieving nearly the same bit error rate that can be provided by the conventional receiver architecture requiring multiple RF/BB chains. The proposed receiver architecture enables multiple transmitter-receiver pairs to simultaneously communicate in the same frequency band without additional bandwidth, thereby increasing the spectral efficiency or capacity, with significantly reduced receiver complexity and power consumption.

We present a new soft handoff scheme that enhances the reliability during soft handoff by increasing the signal distance (Euclidean and/or Hamming) in forward link code division multiple access cellular networks. Each base station participating in soft handoff sends a disjoint subset of the main data stream (called sub-stream) and the mobile receiver reassembles the sub-streams and restores the main data stream. This approach can reduce the data rate per base station by a factor of the number of participating base stations and thereby can increase the signal distance as opposed to the diversity gain. It is shown that the proposed soft handoff scheme is promising for high data rate applications which are the major interests in the next generation cellular networks.

We present a randomized parity forwarding technique in cooperative broadcast networks. A single source sends a common message (codeword) to all nodes, and those nodes that correctly decode the message then generate a parity bit and broadcast it to the remaining nodes. The remaining nodes combine the original codeword from the source with the network-generated parity bits to construct a lower rate, and thus more powerful, error correcting code. The protocol overhead is significantly reduced by allowing each relay node to randomly generate a parity bit independent of other nodes. We present the average probability of decoding error and the energy saving as a function of the number of nodes in the network.

We propose a decentralized random parity forwarding technique in large-scale wireless networks composed of multiple sources, multiple relays, and single destination to enhance the reliability of decoding. The parity bits are generated independently and randomly at the relays and forwarded to the destination. This makes the protocol overhead minimal in coordinating the relay nodes and enables a decentralized network operation. Also, it allows relay nodes to be easily added with little overhead as the network scale increases. The presented model incorporates random distribution of nodes in the network as well as random mobility of nodes that results in a random number of cooperating relay nodes. We analyze the probability of decoding error, and the normalized throughput. We also analyze the outage probability that a selected encoding rule produces an error probability greater than a threshold. We present the energy saving and the coverage area extension provided by the random parity forwarding technique. The effect of multiple antennas at the destination and forward error correcting code at the source are analyzed.

We present a new maximum ratio combining (MRC) technique that performs the maximum ratio combining at the radio frequency (RF) level, thereby requiring only one RF chain and one matched filter. We show that it can achieve the same performance as the conventional MRC technique that performs the combining at the baseband (post-detection), which requires multiple RF chains and multiple matched filters. The proposed approach can be extended to multiple input and multiple output (MIMO) system and significantly reduce the hardware complexity.

The paper investigates and evaluates the application of log-likelihood ratio-based ordering in the decoding stage of amplify-and-forward cooperative spatial multiplexing system. The cooperative spatial multiplexing detects signals transmitted from the source with successive interference cancelation algorithm whose performance varies, depending on the ordering schemes applied. Log-likelihood ratio-based ordering uses and exploits the a posteriori information of the received signal at the destination to get a more accurate final estimation at the decoder output. Based on the evaluation, the authors demonstrate that with marginally extra complexity, log-likelihood ratio based-ordering offers better performance compared to signal-to-noise ratio-based ordering.

We present "concatenated" network coding technique that incorporates multilevel coding across a network of relays in large-scale, multi-hop, noisy wireless networks. A key feature of the proposed approach is that more powerful code can be constructed, hence more errors can be corrected, as the information travels through the network. The decomposition of large-scale network into several small-scale networks and concatenation of small-scale network codes along the route path simplifies both encoding (forwarding) and decoding processes. This is particularly important, because the nodes need to make block encoding based on local information only. This framework is inherently self scalable, in that each new node and each additional hop contribute reliability enhancement. We analyze the probability of decoding error and the normalized throughput as a function of network configuration and number of decoding iterations.

We present a new soft handoff scheme in forward link code division multiple access cellular systems, wherein each base station participating in soft handoff sends only a subset of the main data stream (called sub-stream) and the mobile receiver reassembles the sub-streams and restores the main data stream. This approach can reduce the data transmission rate per base station by a factor of the number of participating base stations at the cost of sacrificing the spatial (macro) diversity that is available in conventional soft handoff system. The key to the proposed technique is to increase the signal distance or the processing gain rather than to obtain additional diversity from multiple base stations on top of multi-path diversity that provides diminishing gain. Power gain and the resulting coverage extension over conventional soft handoff system is analyzed as a function of the number of participating base stations and relative signal strengths from different base stations.

We present a bandwidth-efficient coded cooperative relaying technique that provides a significant coding gain without requiring an increase in bandwidth relative to uncoded cooperative relaying system. The key to the technique is that the redundant bits introduced by the code are accommodated by expanding the relay set, rather than expanding the signal set as in traditional trellis coded modulation. An increase in the number of relays produces additional interference, but its effect can be suppressed by signal processing (decorrelation) and channel coding techniques to produce a positive coding gain without sacrificing data rate or expanding bandwidth. We present the optimum number of relays and the optimal code rate that minimize the end-to-end bit error probability. Additional increase in coding gain by allowing the relay nodes to decode and re-encode is analyzed.

We propose a new detection ordering based on the log-likelihood ratio (LLR) in the iterative nulling and cancellation process of vertical Bell Laboratories layered space-time (V-BLAST) decoding. The motivation for using the LLR is that it provides the reliability information on the maximum a posteriori probability decision. As a result, the error propagation associated with a wrong cancellation can be minimized. Simplified ordering schemes that require a much less computation, but provide a performance virtually identical to the LLR-based ordering, are also provided. The performance of the LLR ordering in the V-BLAST combined with space-time block codes is evaluated.

We propose a new cooperative relaying architecture for delivering aggregated high-rate video data to the destination (base station) in wireless sensor networks. The proposed approach is to make each relay node to detect only a subset (called sub-stream) of the data stream and all relay nodes to forward their sub-streams simultaneously over the same physical channel. Then, multiple receive antennas at the destination allow the sub-streams to be detected separately based on their spatial characteristics. The distinctive benefit of this approach is the reduction of transmit and receive processing requirements on each relay node, while providing significant savings in the transmit and receive energy, particularly in the high spectral efficiency regime. Therefore, the proposed approach is particularly attractive for sending high-rate video data in wireless sensor networks, where each relay can handle only low-rates due to limited resources in terms of energy, bandwidth, hardware, and space (size). The proposed relaying architecture also provides an additional physical layer security mechanism over the traditional network layer security provision mechanisms

We present the optimal Rake finger selection criterion that minimizes the a posteriori probability of symbol error in space-time block coded code division multiple access (CDMA) systems. It can serve as a benchmark for the performance of all a posteriori Rake finger selection criteria. Then we present suboptimal, but more practical, finger selection criteria based on a posteriori symbol error probability bounds, and analyze the bit error probability as a function of constellation sizes and number of resolvable paths. Simulation results show that there is a significant gain over the traditional signal strength-based selection criterion

We propose a new cooperative relaying technique for delivering high-rate data in mobile ad hoc networks. The proposed approach is to make each relay node to detect only a subset (called sub-stream) of the source data stream and all relay nodes to forward their low rate sub-streams simultaneously over the same physical channel. At the destination, multiple receive antennas or RAKE fingers separate the sub-streams and reassemble them based on their spatial characteristics or spreading codes, respectively. The distinctive benefit of this approach is the reduction of transmit and receive processing requirements on each relay node, while providing significant savings in the overall transmit and receive energy, particularly in the high spectral efficiency regime. Therefore, the proposed approach is particularly attractive in situations where each relay can handle only low-rates due to limited resources in terms of energy, bandwidth, hardware, and space (size). The proposed relaying architecture also provides an additional physical layer security mechanism

We present the optimum selection-combining (SC) rule for M-ary signals based on the log-likelihood ratio (LLR) in frequency-nonselective, independent and nonidentically distributed fading channels. The motivation for using the LLR in selecting the diversity branch is that it provides the reliability information of the maximum a posteriori probability decision which minimizes the probability of symbol error. We present coherent and noncoherent optimum SC rules with and without fading information that minimize the probability of symbol error. It is shown that the optimum SC rule provides a significant power gain over the conventional signal-to-noise ratio-based SC rule, and the power gain increases with an increasing number of available diversity branches and decreasing alphabet size. We also present suboptimum SC rules that require less computation, but provide a power gain close to that provided by the optimum SC rule.

We present a generalized selection combining (GSC) of M-ary signals that selects K out of L diversity branches based on the log-likelihood ratio (LLR). The motivation for using the LLR in selecting diversity branches is that the magnitude of LLR provides the reliability of hard decision and the LLR-based hard decision minimizes the bit error probability. It is shown that the proposed LLR-based GSC rule provides a significant power gain over the conventional SNR-based GSC rule, and the power gain increases with decreasing alphabet size and decreasing number of selected branches. We also present suboptimum LLR-based GSC rules that require a less computation, but provide virtually identical performance as the LLR-based GSC rule.

This paper considers the application of space-time coding techniques in DS/CDMA communication systems with multiple transmit antennas. Space-time codes are constructed over the set of possible pseudo noise (PN) sequences rather than standard 2-D signals. Several design examples of these codes with different sequences and slates are presented and possible methods of implementation are suggested. Simulation results indicate that the proposed space-time coded systems provide a significant performance improvement over the reference transmit diversity system. The performance improvement is more pronounced when two receive antennas are employed and grows as the data alphabet M grows.

We propose truncating the transmission power (allocating no power) for symbols with low channel gain, and tagging erasures on the corresponding symbols at the receiver. The motivation is that symbols with low channel gain are highly likely to be in error and yet, if transmitted, consume the energy resource and generate interference to other users. Truncating the power for those symbols has the effect of reducing the interference to other users and allocating more power on symbols with high channel gain (thereby reducing the error probability). Since block codes can correct twice as many erasures as errors, the coded performance can be improved by properly combining the power control with the error-control coding. In this letter, we analyze the performance of the Reed-Solomon-coded multicarrier direct-sequence code-division multiple-access systems with two power-control schemes. We show that the probability of incorrect decoding can be significantly improved by properly combining the power control with the error control coding.

We propose a generalized selection combining (GSC) scheme for binary signaling in which a subset of diversity branches providing the largest magnitude of log-likelihood ratio (LLR) are selected and combined. It is shown that the bit-error probability with maximum ratio combining (MRC) or square-law combining of L branches is identical to that with LLR-based GSC of L/2 branches. We also propose a simple, but suboptimal, GSC based on a noncoherent envelope detection and discuss its potential advantages over the conventional signal-to-noise-ratio-based GSC and MRC.

We propose a new detection ordering for the V-BLAST. The main idea is to detect and cancel sub-streams in order of the magnitude of log-likelihood ratio (LLR), i.e. the symbol with the largest magnitude of LLR is detected first. The motivation is that the reliability of data decision increases with increasing magnitude of LLR. As a result, the error propagation associated with a wrong decision and the resulting error probability for the remaining sub-streams can be minimized. It is shown that the proposed LLR-based ordering significantly outperforms the conventional SNR-based ordering. Simplified LLR-based ordering and envelope-based ordering that require a much less computation, but provide a performance virtually identical to the LLR-based ordering, are also proposed.

We present the difference threshold test (DTT) as a method for generating reliability information for M-ary signaling with coherent detection. The proposed DTT declares an erasure whenever the difference between the shortest Euclidean distance and the second shortest Euclidean distance from the received signal is less than a threshold. We show that the DTT is an approximation of the Bayesian test, and, for binary signaling, it is equivalent to the Bayesian test. We also extend the DTT for L-fold diversity systems. The performance of Reed-Solomon (RS) codes with errors-and-erasures decoding is analyzed when the DTT and the conventional SNR threshold test are applied.

We present the difference threshold test (DTT) for M-ary orthogonal frequency shift keying (FSK) signaling in Rayleigh flat fading channels. The proposed DTT declares an erasure whenever the difference between the largest and the second largest energy detector output does not exceed a fixed threshold. We show that the DTT is an approximation of the Bayesian erasure test, but provides almost the same performance as the Bayesian erasure test. For (7,3) and (31,15) Reed-Solomon (RS)-coded systems, the DTT provides power gains of 0.8 dB and 0.4 dB over the ratio threshold test (RTT), respectively. We prove that the limiting performance of the DTT approaches that of the RTT for very large M.

We propose a generalized selection combining (GSC) scheme for binary signaling in which M diversity branches providing the largest magnitude of log-likelihood ratio (LLR) are selected and combined. The bit error probability provided by LLR-based GSC serves as a lower bound on the bit error probability provided by any GSC techniques. We also propose a suboptimal GSC based on a noncoherent envelope detection. We derive the bit error probability with LLR-based and envelope-based GSC techniques and examine their power gains over the conventional SNR-based GSC technique. We show that the bit error probability with maximum ratio combining or square-law combining of L branches is identical to that with LLR-based GSC of L/2 branches.

The optimum receive antenna selection combining rule that minimizes the bit error probability is presented. It is derived from a general relationship between the bit error probability and the log-likelihood ratio (LLR), and selects the receive antenna providing the largest LLR magnitude. The optimum selection combining rule is applied to single transmit (Tx) antenna and space-time block code (STBC) systems, with N/sub R/ receive (Rx) antennas, and the bit error probability is derived for BPSK signaling in Rayleigh flat fading channels. A suboptimum selection combining rule based on noncoherent envelope detection is also presented and analyzed. For STBC systems, the optimum generalized selection combining in which M(/spl les/ N/sub R/) Rx antennas providing the largest LLR magnitude are selected and combined is presented.

We present the optimum selection combining for M-ary signaling based on the log-likelihood ratio that minimizes the probability of symbol error. Then, we present the noncoherent optimum selection combining that does not require knowledge of the signal phases on each branch. Numerical results indicate that a significant gain over the SNR-based selection combining can be provided by the proposed optimum selection combining. Finally, we present a suboptimum selection combining that requires a lower complexity, but provides a power gain close to that of the optimum selection combining.

We propose a new generalized selection combining (GSC) scheme that selects m diversity branches out of L (/spl ges/m) diversity branches based on the magnitude of the log-likelihood ratio (LLR), which, for BPSK signals, is proportional to the product of the fading amplitude and the matched filter output. The proposed GSC is shown to provide a significant power gain over the conventional GSC which selects diversity branches based on signal-to-noise ratio. The proposed GSC scheme for m=3 is found to be only 0.3 dB inferior to the maximal ratio combining scheme (m=L), when L=8, in a Rayleigh fading channel.

Transmission power adaptations are considered in a space-time block code (STBC) system utilizing feedback channel gain information. We investigate the optimal power adaptation scheme that minimizes the average BER subject a fixed average transmission power constraint. We present the power gain provided by the optimal adaptation scheme over the conventional STBC without power adaptation. The power gain provided is found to be 13.8 dB at BER of 10/sup -5/ in a Rayleigh fading channel. Also, we analyze the performance of STBC system with optimal truncated power adaptation which compensates for fading above a certain fade depth: below the cutoff level data transmission is suspended (ie, outage condition is declared). Finally, we propose a simple adaptation scheme for STBC systems based on two-bits feedback information that provides a power gain of 4.3 dB at BER of 10/sup -5/.

Partial successive interference cancellation is considered in hybrid DS/FH spread-spectrum multiple-access (SSMA) systems. We first show that the lowest BER attained by employing full interference cancellation in DS/SSMA systems can almost be achieved by employing a partial interference cancellation in hybrid DS/FH systems. The reduction in the number of cancellations translates into an alleviation of correlator speed requirements and a reduction in delays incurred in interference cancellations. The optimal number of frequency slots that minimizes the BER is investigated as a function of the number of interference cancellations. The effect of imperfect power control on the BER is investigated.

We propose a new selection diversity scheme, called |ar|-selection diversity, that selects the branch providing the largest magnitude of log-likelihood ratio (LLR). The LLR for BPSK signals in fading channels is found to be proportional to the product of the fading amplitude and the matched filter output after phase compensation. The proposed |ar|-selection diversity scheme is shown to be optimal in the sense of minimizing the bit error rate (BER), and outperform existing selection diversity schemes. We also propose a suboptimal selection diversity scheme, called |aw|-selection diversity, that does not require a phase compensation in the selection process, thereby significantly reducing implementation complexity. We show that the proposed |ar|-selection and |aw|-selection diversity schemes exhibit significant power gains over existing selection diversity schemes in Rayleigh fading channels.

We consider a combined power/code rate adaptation in Reed-Solomon (RS) coded frequency-hopped spread-spectrum multiple access (FH/SSMA) communications, where the transmission power and code rate are adapted simultaneously relative to the channel traffic and channel fading. We investigate the optimal transmission strategy that minimizes the required signal-to-noise ratio for a given error performance, and the performance improvement provided by the optimal strategy over adaptive code rate control and adaptive power control. We show that the combined power/rate control provides an asymptotic power gain of 5.67 dB over adaptive code rate control.

Power and rate adaptations with diversity are considered for M-ary orthogonal signals in a frequency-nonselective Rayleigh fading channel. We derived the minimum required E~/sub b//N/sub 0/ for a given probability of error, the maximum average data rate, and the outage probability, when maximal-ratio combining is performed with an imperfect channel estimation. We analyzed the effects of channel estimation errors on the required E~/sub b//N/sub 0/ and outage probability, as a function of diversity order and adaptation methods. The relative benefits of rate and power control techniques are further presented in terms of channel estimation error, diversity order, and outage probability. The minimum required E~/sub b//N/sub 0/ with Reed-Solomon codes is also presented for comparison purposes.

We propose the multicarrier on-off keying (MC-OOK) as a bandwidth-efficient modulation method for frequency-hopped multiple-access (FHMA) communications. The motivation for using MC-OOK is that a more bandwidth-efficient modulation scheme allows a larger number of frequency slots, and thus provides a higher immunity against multiple-access interference in FHMA systems. We analyze the average bit-error probability in slow frequency-nonselective Rayleigh fading channels with background noise. We find that the capacity gain that MC-OOK/FHMA system provides over the MFSK/FHMA system in an interference-limited region is more than 2.5 when the modulation alphabet size M is 8, and even a higher capacity gain can be obtained with a larger M.

We consider combined rate and power adaptations in direct-sequence code-division multiple-access communications, where the transmission power and the data rate are adapted relative to channel variations. We discuss the power gain that the combined adaptations provide over power adaptation. Then, we consider an integrated voice and data transmission system that offers a constant bit rate voice service, using power adaptation and a variable bit rate data service with rate adaptation. We present an expression for the required average transmission power of each traffic type having different quality-of-service specifications and discuss the capacity gain over power adaptation for voice and data.

We investigate the average information rates attained by adapting the transmit power and the information rate relative to channel variations in code division multiple access communication systems. Our results show that the rate adaptation provides a higher average information rate than the power adaptation for a given average transmit power, and the rate increase when using rate adaptation is more significant for channels with a faster decaying multipath intensity profile and weaker line-of-sight component.

The asymptotic performance of Reed-Solomon coded M-ary orthogonal signaling with ratio-threshold test (RTT) type demodulation in a Rayleigh fading channel is considered. We show that the minimum E~/sub b//N/sub 0/ needed for error-free communication is eln2 (2.75 dB) with RTT, and 4.79 (6.8 dB) with hard decision. The optimum code rate that minimizes the required E~/sub b//N/sub 0/ is e/sup -1/ with RTT and 0.46 with hard decision, and the optimum ratio threshold approaches 1 for large M. Next, we investigate the fundamental limit in direct-sequence spread-spectrum multiple-access (DS/SSMA) system employing an M-ary orthogonal code of length N=Mm, which is obtained by spreading every row of an M/spl times/M Hadamard matrix with a user-specific random sequence of length N. We derive the minimum E~/sub b//N/sub 0/ for error-free communication as a function of the number of users, the optimum code rate that minimizes E~/sub b//N/sub 0/, and the maximum limit on the total information transmission rate.

Nonorthogonal binary frequency-shift keying is considered in frequency-hopped multiple-access communication systems with Reed-Solomon coding. The effect of tone spacing on the average number of successfully transmitted information bits per unit time per unit bandwidth (called normalized throughput) is examined in Rayleigh fading channels. The tradeoff among tone spacing, code rate, and number of frequency slots in maximizing the normalized throughput is examined, keeping the total bandwidth fixed. The optimal tone spacing, code rate, and number of frequency slots in terms of the number of users and E~/sub b//N/sub 0/ is also discussed. The throughput gain attained by using the optimal tone spacing becomes more significant as the number of users is increased.

The asymptotic performance of Reed-Solomon (RS)-coded M-ary orthogonal signaling with ratio-threshold test (RTT) type demodulation in a Rayleigh-fading channel is considered. We show that the minimum E~/sub b//N/sub 0/ needed for error-free communication is eln2 (2.75 dB) with RTT, and 4.79 (6.8 dB) with hard decisions. The optimum code rate that minimizes the required E~/sub b//N/sub 0/ is e/sup -1/ with RTT and 0.46 with hard decision, and the optimum ratio threshold approaches 1 for large M. Next, we investigate the fundamental limit in a direct-sequence spread-spectrum multiple-access (DS/SSMA) system employing an M-ary orthogonal code of length N=Mm, which is obtained by spreading every row of an M/spl times/M Hadamard matrix with a user-specific random sequence of length N. We derive the minimum E~/sub b//N/sub 0/ for error-free communication as a function of the number of users, the optimum code rate that minimizes E~/sub B//N/sub 0/, and the maximum limit on the total information transmission rate. Then, we consider a multirate DS/SSMA system, where a population of users simultaneously transmit at different power levels a variety of traffic types of different information rates. We derive the minimum required E~/sub B//n/sub 0/ and the optimum code rate for each traffic type.

In this paper, we propose a simple packet combining scheme in frequency-hopped spread spectrum multiple access (FH/SSMA) communication networks, which makes a tone-by-tone logical AND operation on the previously combined packet and the currently received (retransmitted) packet. The packet error probability is analyzed in the presence of multiple access interference (MAI) with AWGN or Rayleigh fading. It is found that the number of simultaneous users can be increased almost by a factor of two as compared to the conventional scheme, and the performance improvement becomes more significant, as the number of combined packets is increased. It is also found that for the packet error probability of 10/sup -2/ and M=8, a 2-4 dB gain in E/sub b//N/sub 0/ can be obtained over the conventional scheme in the AWGN and Rayleigh fading channels, and the gain increases as M increases.

There has been increased interest in the use of direct-sequence code-division multiple-access (DS/CDMA) for wireless communication systems. We find that the asymptotic bit-error probability (BEP), P_b, of a convolutionally coded code-division multiple-access (CDMA) system in a frequency-selective Rayleigh-fading channel depends on the length of the shortest error event path and the product of symbol distances along that path. Based on this observation, we propose a new spreading scheme that maximizes the length of the shortest error event path. It is shown that the proposed scheme yields an improvement of 1.0-1.3 dB at P_b = 10^(-5) over the conventional convolutionally coded CDMA system, and even a higher improvement can be achieved as the required BEP is decreased.

A two-dimensional array code, referred to as product code, has been extensively used to combat the errors in digital image recording systems such as digital VCR. An error-control coding scheme for multispeed play of digital video cassette recorder (DVCR) is proposed and analyzed. The proposed coding scheme is shown to yield a significant performance improvement over the conventional scheme with only a minor or no increase, depending on the play mode, in decoding time. A computer simulation is done on DCT-based quantized images to verify our analysis.>

A transmission policy for frequency-hopped spread-spectrum random-access communication systems in which the retransmission of a blocked packet at each station is determined as a function of that station's own collision experience is examined. For stability considerations and for channel throughput increase, the information packet is encoded by a Reed-Solomon code. An equilibrium analysis is used to show that undesirable bistable behaviour can be avoided if packets are rejected after a certain number of transmission attempts and the code rate is adjusted accordingly. The region of code rate and number of transmission attempt pairs that guarantees the network stability are investigated. The packet rejection probability, average packet delay, and maximum stable throughput are evaluated.>

The optimal packet arrival distribution at the input of the channel that maximises the channel throughput is found. This is used to find the optimal retransmission policy and the maximum channel throughput. A generalized channel model where simultaneous transmission of m packets is successful with probability P/sub c/(m) is considered. Most previous studies have considered the case P/sub c/(m)=0 for m >or= 2 and P/sub c/(1)=1. The channel throughput obtained with the optimal arrival distribution (i.e., the optimal multiaccess protocol) and that with the Poisson arrival distribution (i.e., the ALOHA protocol) are compared for two specific channel models. Results are presented for a frequency-hopped spread-spectrum multiple-access system.>

A method is presented for stabilizing slotted ALOHA frequency-hop communication networks by controlling code rate. In particular, the stabilization of a fully connected network in which a finite number of transmitter-receiver pairs exchange packets of information encoded by Reed-Solomon codes is considered. A principle of flow balance to stability analysis is adopted, and it is shown that network stability can be ensured by controlling code rate. The requirement on code rate for ensuring network stability is examined. In addition, the mean delay and the mean channel throughput of the network are discussed.>

The authors consider a multiple-access frequency-hopped spread-spectrum communication system with Reed-Solomon codes. The performance measures of interest are an achievable region and the channel throughput. The achievable rate region is the set of all pairs of code rate and number of users for which communication is possible with error probability below a fixed value. The throughput measures the expected number of successful codeword transmissions per unit bandwidth. Two models of interference are considered. For these two models, the authors determine the optimal number of users for a given bandwidth and the optimal rate Reed-Solomon code that maximize the throughput. They also determine the achievable region for these models.>