We consider the scenario in which multiple sensors send spatially correlated data to the fusion center (FC) via independent Rayleigh-fading channels with additive noise. Assuming that the sensor data is sparse in some basis, we show that the recovery of the signal can be formulated as a compressive sensing (CS) problem. To model the scenario where sensors operate with intermittently available energy that is harvested from the environment, we propose that each sensor transmits independently with some probability, and adapts the transmit power to its harvested energy. Due to the probabilistic transmissions, the elements of the equivalent sensing matrix are not Gaussian. Besides, since the sensors have different energy harvesting rates and different sensor-to-FC distances, the FC has different receive signal-to-noise ratios (SNRs) for each sensor, referred to as the inhomogeneity of SNRs. Thus, the elements of the sensing matrix are also not identically distributed. We provide theoretical guarantees on the number of measurements for reliable reconstruction, by showing that the sensing matrix satisfies the restricted isometry property (RIP), under some mild conditions. We then compute an achievable system delay under an allowable mean-squared-error (MSE). Furthermore, using techniques from large deviations theory, we analyze the impact of inhomogeneity of the SNRs on the so-called k-restricted eigenvalues, which governs the number of measurements required for the RIP to hold. Our analysis is corroborated by numerical results.

We consider a cognitive spectrum sharing system on an interference channel with a cognitive relay (IFC-CR) assisting both the primary and secondary users in forwarding their messages to the respective destination nodes. The CR uses a successive interference cancelation scheme to decode the primary and secondary messages after a first transmission phase. The CR performs power allocation and in the second transmission phase, forwards a linear weighted combination of the decoded primary and secondary messages. We demonstrate that with a properly designed power allocation, secondary spectrum sharing is achieved and at the same time a better performance can be achieved for the primary user than the case without spectrum sharing. The proposed spectrum sharing scheme further does not require any non-causal knowledge of the primary message at the secondary user or at the CR.

In this paper, we consider a hidden terminal scenario where two transmitters A and B, hidden to each other, wish to communicate to a common access point, AP. When a collision occurs at AP, due to the inherent asynchrony between the colliding packets, the mutual interference between them is effectively decreased. This achieves a higher signal-to-interference-plus-noise (SINR) ratio which improves the probability of successfully decoding both colliding packets through conventional successive interference cancellation (SIC). When neither colliding packet can be decoded first through SIC, we propose an enhanced SIC (ESIC) scheme. The proposed decoding scheme does not require synchronization, coordination or power control between the transmitters or a sophisticated coding design. By exploiting the inherent asynchrony between the two colliding packets, there exists, with high probability, an interference-free chunk together with an interfered chunk in a packet ready for decoding. Thus it is still possible for both colliding packets to be recovered eventually from a single collision. Our results demonstrate that through the proposed ESIC scheme, both colliding packets can be recovered with a higher probability thus improving the system throughput.

In this paper, we propose a two-phase protocol based on cooperative relaying for a secondary system to achieve spectrum access along with a selective relaying primary system. The primary system comprises of a transmitter-receiver pair PT-PR and M relays Ri, i G {1,2,⋯ , M}. The secondary system is a multi-user system with N transmitters Ri, i ϵ {M +1, M + 2, ⋯ , M + N } which intend to communicate with a common receiver SR. In the proposed protocol, terminals Ri, i ϵ M1= {1, 2, ⋯ , M + Q} are designated as possible candidates for assisting the primary system while the remaining secondary transmitters Ri', i' ϵ M2= {M + Q + 1, M + Q + 2, ⋯ ,M + N} are chosen as possible candidates for secondary spectrum access, where 0 ≤ Q ≤ N. The relaying terminal Rp, p ϵ M1which achieves the request target rate for the primary system and has the best channel to PR, is first selected from M1to serve as a decode-and-forward (DF) relay for the primary system. With the cooperation of Rp, the primary system is able to tolerate some interference lower than a certain threshold in the relaying phase, without degrading its outage performance. The secondary transmitter Rs, s ϵ M2which satisfies this interference constraint and optimizes the outage performance for the secondary system, is then selected from M2to access the spectrum band simultaneously when Rpis relaying the primary signal. Analytical and simulation results confirm the efficiency of the proposed spectrum sharing protocol. We show that there exists an optimal value for Q and both primary and secondary systems are able to achieve better outage performance with increasing N.

We consider spectrum sharing in a cognitive radio network where a secondary system co-exists with an automatic repeat-request (ARQ)-based primary system. A cooperate-and-access spectrum sharing protocol is proposed where the secondary system alternates between cooperation and access modes. In the cooperation mode, the secondary system serves as a relay to assist the primary transmission, and in return accumulates credits. The credits allow the secondary system to gain spectrum access by exploiting the ARQ retransmissions of the primary system. We show analytically that through the proposed credit system, as long as the credits accumulated in cooperation mode compensate for the degradation in primary performance during access mode, an equal or higher average throughput is achieved for the primary system than in the case without spectrum sharing, while providing spectrum access opportunities for the secondary system.

In this paper, we propose an opportunistic spectrum sharing protocol that exploits the situation when the primary system is incapable of supporting its target transmission rate. Specifically, the secondary system tries to help the primary system to achieve its target rate via two-phase cooperative OFDM relaying, where the secondary system acts as an amplify-and-forward relay for the primary system by allocating a fraction of its subcarriers to forward the primary signal. At the same time, the secondary system uses the remaining subcarriers to transmit its own signal, and thus gaining opportunistic spectrum access. As a part of the protocol, if the primary system finds that outage will occur even when the secondary system serves as a pure relay, the primary system will cease transmission and the secondary system will be granted access to the primary spectrum. We study the joint optimization of the set of subcarriers used for cooperation, subcarrier pairing, and subcarrier power allocation such that the transmission rate of the secondary system is maximized, while helping the primary system, as a higher priority, to achieve its target rate. Simulation results demonstrate the performance of the proposed spectrum sharing protocol as well as the win-win solution for the primary and secondary systems.

In this paper, we have designed and developed a testbed for proof-of-concept demonstration and performance assessment of cooperative spectrum sharing (CSS) protocols. The performance of the testbed has been validated by obtaining both quantitative as well as qualitative results. Quantitative results are obtained by measuring the packet error rates for both primary and secondary systems during different times of the day whereas qualitative results are shown by utilizing a CSS protocol to successfully transmit two different images from primary transmitter (PT) to primary receiver (PR) and secondary transmitter (ST) to secondary receiver (SR) respectively. A parameter known as spectrum access probability which quantifies the probability of spectrum access for the secondary system is also measured.

In this paper, we will analyze how different amount of receiver side information (RSI) available at the receivers of a broadcast channel will affect the overall network throughput. Two transmission schemes, namely random linear network coding (RLNC) and round robin scheduling (RRS), are considered. Taking into account the differing amount of RSI available at each receiver, closed-form expressions of network throughput and asymptotic throughput at high SNR are obtained for a broadcast channel. Our results show that the asymptotic throughput of RLNC is always no worse than RRS no matter how much RSI is available at each receiver. With a sum constraint for the overall arrival rate of receiver side information in the broadcast channel, we show that the the maximum throughput is achieved for RLNC if each receiver accumulates the same amount of RSI.

In this paper, we propose a cooperative spectrum sharing protocol (CSSP) between two overlapping static ad hoc wireless networks where the primary and secondary networks consist of n and m randomly distributed nodes respectively. The secondary network achieves spectrum access along with the primary network by allowing its nodes to relay the primary traffic. Taking advantage of the broadcast nature of wireless channels, the secondary nodes are able to forward primary and secondary packets simultaneously by transmitting a superimposed signal. We analyze the throughput and delay scaling performance of the proposed protocol and show that given m ≥ n, the primary network is able to achieve a per-node throughput scaling which is better than that of a stand-alone network with n nodes. At the same time, the secondary network achieves the same throughput scaling as a stand-alone network with m nodes. We also derive the throughput-delay tradeoff for both the primary and secondary systems in this scenario.

In this study, the authors consider a cognitive radio scenario and focus on the spectrum efficiency of sensing-transmission protocols for a secondary dual-hop relay system. A straightforward dedicated sensing protocol is first considered as a benchmark, where sensing is performed in dedicated sensing periods at both the source (S) and the relay (R) before their respective transmissions. This, however, leads to a substantial loss in spectrum efficiency for the secondary system. In view of the spectrum efficiency loss in the dedicated sensing protocol, the authors propose an alternative approach, namely simultaneous sensing protocol. In this protocol, sensing is only performed at S, during the period when R transmits to destination (D), by cancelling out the self-interference component that is known a priori. The authors derive the closed-form expression of the average probability of detection for the proposed simultaneous sensing protocol. Furthermore, by deriving the average collision time and average utilisation time for both the dedicated and simultaneous sensing protocols, the authors show that the simultaneous sensing protocol significantly improves the spectrum efficiency for the secondary system and also achieves a higher overall spectrum utilisation of the spectrum band, compared to the dedicated sensing protocol.

In this paper, we consider a wireless multicast network with multiple sources, relays, and destinations. We adopt a multi-hop decode-and-forward relay protocol such that two canonical subnetworks are relevant, namely broadcast channel with receiver side information (BC-RSI) and orthogonal multiple access channel with correlated sources and receiver side information (MAC-CS-RSI). A joint network and channel coding (JNCC) strategy is proposed by exploiting ARQ, RSI, and correlated sources. The proposed JNCC strategy does not require the knowledge of RSI nor any transmit channel state information, such that each transmitter simply performs retransmissions until the intended receivers have accumulated enough mutual information to successfully decode all desired messages. This successful decoding is then conveyed from the receivers to the respective transmitters via an acknowledgement message. To measure the performance of the proposed JNCC strategy with ARQ, we derive closed-form expressions of network throughput by applying the renewal-reward theorem. Analytical results show that the proposed JNCC strategy outperforms, in terms of network throughput, the conventional separate network and channel coding strategy with random linear network coding.

Two-path or successive relaying has recently emerged as a promising cooperative communication protocol to improve spectral efficiency in half-duplex relaying networks. In this paper, we consider decode-and-forward (DF) version of the two-path relaying protocol. We analyze the fundamental performance of this protocol in terms of the diversity-multiplexing tradeoff (DMT). We first derive the DMT for this protocol, where perfect decoding at the relays is assumed, and show that it approaches the 3 x 1 multiple-input single-output (MISO) DMT. We then remove the assumption of perfect decoding at the relays and derive the closed-form expression of the achievable DMT based on the relative distances between nodes. Specifically, we found that for sufficiently long transmission length, if the average source-relay SNR is at least 2.5 times (measured in dB) of other links, the 3 x 1 MISO DMT is achieved. Successive interference cancellation at the relays is also proposed to further improve the performance of the DMT.

Although much research has been devoted to the theoretical performance evaluation of cognitive spectrum sharing (CSS) protocols, there are few measurement results available to demonstrate the practical performance of such protocols. In this paper, we have designed and developed a testbed for proof-of-concept demonstration and performance assessment of our proposed CSS protocol. The packet error rate (PER) for both primary and secondary systems are measured to quantify their respective performance. Spectrum access probability for the secondary system is also measured. Measurement results proved that the proposed CSS protocol is able to assist the primary system to achieve a better PER and at the same time allows spectrum access for the secondary system.

In this paper, we propose a two-phase protocol based on cooperative relaying for a secondary system to achieve spectrum access along with a primary system. The primary system comprises of a transmitter-receiver pair PT-PR, and the secondary system comprises of M transmitter-receiver pairs STi-SRi, i ∈ {1,2,⋯M}. The secondary pair STb-SRbwhich is able to provide the best performance for the primary system, is selected to access the spectrum, with STbserving as a cooperative relay for the primary system. In the first transmission phase, PT transmits the primary signal to PR, which is also received by STband SRb, where it is decoded. At STb, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions α and (1-α) of the available power to the primary and secondary signals respectively. This combined signal is then broadcasted by STbin the second transmission phase, and PR combines the signal it received in the two phases to decode for the primary signal. Theoretical and simulation results confirm that the outage performance for both primary and secondary systems are improved with a larger M by using the proposed scheme.

In this paper, an amplify-and-forward (AF) two-path half-duplex relaying scheme is considered in which one of the relays additionally performs inter-relay interference cancellation. We first generalize lower bounds for the diversity-multiplexing tradeoff (DMT) of an arbitrary block lower triangular channel matrix. We then characterize the diversity-multiplexing tradeoff for the AF two-path relaying scheme and show that the DMT achieves the multiple-input single-output (MISO) upper bound. The analysis also demonstrates that, with a careful choice of the coding strategy, the DMT of this scheme is achievable for finite codeword lengths. We then propose using an equivalent linear space time code at the source, which does not require any form of channel state information, as a simple and effective coding strategy to achieve the full DMT of the scheme. From the DMT perspective, the proposed AF two-path relaying with the equivalent linear space time coding outperforms existing schemes. Our analysis is then extended to the slotted-amplify-and-forward (SAF) scheme with multiple relays, where we provide a stronger result by deriving the DMT while taking into account inter-relay interference.

In this paper, we propose a two-phase protocol based on cooperative relaying for a secondary system to achieve spectrum access along with a primary system. The primary system comprises of a transmitter-receiver pair PT-PR, and the secondary system comprises of M transmitters STi, i ∈ {1, 2,..., M} and a common receiver SR. The secondary transmitter STpwhich achieves the request target rate for the primary system is selected to serve as a decode-and-forward (DF) relay for the primary system. With the cooperation of STp, the primary system is able to tolerate interference lower than a certain threshold in the relaying phase, without degrading its outage performance. The secondary transmitter STs, which satisfies this interference constraint and provides the optimal outage performance for the secondary system, is then selected to access the spectrum band simultaneously when STpis relaying the primary signal. Theoretical and simulation results confirm the efficiency of the proposed spectrum sharing protocol, and we show that both primary and secondary systems are able to achieve better outage performance with increasing M.

In a typical network coding scenario, a node has to broadcast a set of messages to a group of receiver nodes who have already received a subset of the messages through other links. In this paper, we will first present the achievable rate region for this broadcasting scenario, and then extend the result to the case with retransmissions. With the proposed nonlinear network coding strategy, the achievable rate region can be achieved without requiring the exact knowledge of a priori information available at the receiver nodes. The broadcasting node simply performs retransmissions with independent codebooks until every receiver node has received the whole set of messages. Through the analysis of network throughput, we will show that each receiver node is able to effectively accumulate mutual information over the multiple transmissions thus achieving higher overall throughput than the conventional random linear network coding strategy.

Using relays to extend the coverage of base-stations in cellular systems has been of interest in recent years as it can reduce the cost of installing more base-stations and yet cater to mobile terminals within a wider coverage area. There have been recent advances where two or more half duplex relay stations are used to recover the loss of bandwidth due to the use of half duplex relays. However, such schemes would not be beneficial in cases where the inter-relay channel is strong, and the relays start interfering each other. In this paper, we study the use of beamforming techniques to resolve the problem of inter-relay interference.

The performance of modern communication transmitters utilising multi-carrier modulation techniques is highly sensitive to non-linear distortions arising mainly from the high-power amplifier (HPA). In addition, the wideband characteristics of multi-carrier signals result in frequency-dependent distortions, typically known as memory effects. This study aims to analytically evaluate the impact of the distortion induced by non-linear HPA with memory on a multi-carrier signal exemplified by orthogonal frequency division multiplexing (OFDM). The behavioural model of HPA considered for theoretical analysis is a memory polynomial model, which is a truncated form of the Volterra series. In the theoretical framework developed, this study shows that memory in HPA considerably degrades the performance of OFDM in terms of symbol error rate (SER), and the distortion itself can be canonically characterised by a complex attenuation component and a non-linear noise component. Closed-form expressions for SER in additive white Gaussian noise channel are derived and the SER for fading channel is approximated by the adaptive Gauss–Kronrod quadrature method. Simulation results are shown for a realistic HPA, based on the Wiener–Hammerstein model, and compared with the analytical results to validate the proposed analysis.

The authors first propose a new class of full-rate full-diversity quasi-orthogonal space time block code (QO-STBC), namely QO-STBC with blind precoding (BP-QO-STBC). Based on this code, a novel open-loop multiple-input multiple-output (MIMO) multi-user downlink transmission scheme is derived. Presuming M blocks of BP-QO-STBC (which could be of different code lengths) are transmitted from the access point simultaneously, thus achieving a multiplexing gain of M, we show that the multiplexed signal can be separated by any user with only mR≥M receive antennas, which is much smaller than that required by conventional linear schemes. The proposed scheme is extendable by simple iterative construction to an arbitrary number of transmit antennas. By exploiting the special structure of BP-QO-STBC, we derived two decoding algorithms with different levels of complexities, namely an optimal maximum likelihood decoder that achieves the lowest decoding complexity known for all full-rate full-diversity QO-STBC and a suboptimal linear decoder with even lower complexity. These two decoders combined with the simple construction method of BP-QO-STBC provide flexible tradeoffs between complexity and performance, as well as between diversity and multiplexing gains. A comparison between the proposed scheme and random beamforming in terms of bit error rate and achievable sum throughput is shown via simulation, and the results support our proposed scheme as a better practical candidate for high-speed wireless network.

We propose a two-phase protocol based on cooperative decode-and-forward relaying for a secondary system to achieve spectrum access along with a primary system. The primary and secondary systems comprise of a transmitter-receiver pair, PT-PR and ST-SR, respectively. In the first transmission phase, PT transmits the primary signal to PR, which is also received by ST and SR, where it is decoded. At ST, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions alpha and (1 - alpha) of the available power to the primary and secondary signals respectively. This combined signal is then broadcasted by ST in the second transmission phase. We show that as long as ST is located within a critical radius from PT, there exists a threshold value for alpha above which the outage probability of the primary system will be equal to or lower than the case without spectrum sharing. We also determine the outage probability achieved by the secondary system. Theoretical and simulation results confirm the efficiency of the proposed spectrum sharing scheme.

In this paper, the average sum rate of two-way amplify-and-forward (AF) half-duplex relaying system is analyzed. To this end, we first derive the harmonic mean of two independent gamma distributed random variables which have the same shape parameter but different scale parameters. By deriving tight upper and lower bounds for the average sum rate of two-way relaying, we verify that two-way relaying can significantly recover the spectrum efficiency loss of one-way relaying. We also extend the two-way AF half-duplex relaying to the case where source and destination terminals both transmit Alamouti's orthogonal space time block code (OSTBC) utilizing two antennas and the relay has only one antenna. By deriving both upper and lower bounds for the average sum rate as well as an upper bound for the pairwise error probability (PEP) for the proposed two-way OSTBC scheme, we show that the average sum rate is further improved compared to the single antenna case and a diversity order of two is also achieved. Furthermore, optimal power allocations under a global power constraint for two-way relaying with single antenna and the proposed two-way OSTBC scheme are derived analytically.

This paper analyzes the outage performance of cooperative protocols for the two-way relaying model in which a half-duplex relay assists in the bi-directional communication of two terminals. We first define the outage events and derive closed form results for the outage probabilities of conventional nonadaptive Amplify-and-Forward (AF) and Decode-and-Forward (DF) two-way relaying protocols.We then consider a simple adaptive protocol in the two-way relaying scenario, which switches between AF and DF depending on the decodability of the two bi-directional data streams at the relay. We also derive the outage probability for this adaptive scheme in closed form expressions, and our results show that it always outperforms the non-adaptive schemes. All the closed form results derived in this paper are applicable to arbitrary channel gains between terminals.

In this paper, we consider a network consisting of one source, one destination and two relays, under a half duplex constraint. We analyze an amplify-and-forward (AF) two-path relaying scheme where one of the relays additionally performs inter-relay interference cancellation. With this inter-relay self interference cancellation, we show that degradation in performance can be significantly reduced when inter-relay channel gain increases. By treating the AF two-path relaying as an equivalent MIMO space time code, we derive an upper bound for the pairwise error probability (PEP) of this system. Previous works indicate that only a diversity order of two can be achieved even though physically there are three possibly independent spatial paths to the destination. From our analysis of the PEP, we analytically prove and identify the reason to the limited diversity order of two. We then propose a simple but novel precoding scheme which allows the system to achieve a full diversity order of three while maintaining the spectral efficiency gain of the two-path relaying protocol. A robust precoding design to achieve full diversity order with high coding gain is also proposed.

This paper analyzes the effects of nonlinear high power amplifier (HPA) with memory on an orthogonal frequency division multiplexing (OFDM) signal, by modeling the nonlinear HPA as a memory polynomial model with sparse delay taps. In the theoretical framework developed, we show that the in-band distortion due to nonlinear HPA with memory affects each subcarrier differently and the distortion itself can be canonically characterized by a complex attenuation component and nonlinear noise component. Analytical expressions for the complex attenuation and nonlinear noise are derived. From the expressions, a complete analytical approach to evaluate signal to noise ratio and probability of error for each subcarrier in an additive white Gaussian noise (AWGN) channel is obtained and illustrated using a M-QAM OFDM system. A comparison between theoretical and simulated results is also presented to verify the accuracy of our analysis.

In this paper, we derive tight upper and lower bounds for the average sum rate of two-way amplify-and-forward (AF) half-duplex relaying, which show that two-way AF half-duplex relaying can significantly mitigate the spectral efficiency loss of conventional one-way AF half-duplex relaying. We then extend the AF half-duplex two-way relaying to the case where source and destination terminals both transmit Alamouti's orthogonal space time block code (OSTBC) utilizing two antennas and relay has only one antenna. We derive both upper and lower bounds for the average sum rate as well as an upper bound for the pair-wise error probability (PEP) for the proposed OSTBC scheme. We also find the optimal power allocation for both two- way relaying schemes analytically. Our theoretical analysis and numerical simulation results show that higher average sum rate compared to the single antenna case and diversity order of two are achieved by the proposed OSTBC scheme.

In this paper, we analyze a full rate cooperative communication system using amplify-and-forward (AF) two-path relaying scheme with inter-relay interference cancellation at the relay. By treating AF two-path relaying as an equivalent MIMO system, we derive the pairwise error probability (PEP) of this system. Given one source node, two half duplex relay nodes, and one destination node, all equipped with single antenna, our theoretical analysis and simulation results show that diversity order of 2 can be achieved by this system. Furthermore, with inter-relay interference cancellation, degradation in performance can also be significantly reduced when inter-relay channel gain increases. Our analysis also shows that diversity order of the system will not be affected by the magnitude of this inter-relay channel gain.

As the wireless channel is constantly changing, MIMO-OFDM eigenmode transmission is extremely vulnerable to the presence of feedback delay which is unavoidable in a practical system. Under such imperfect conditions, the inter-eigenmode interference can be removed through the use of the MMSE interference canceller. However, to the best of our knowledge, the performance of MIMO-OFDM eigenmode with MMSE interference canceller has not been proven by experimental results. In this paper, we present experimental results for the bit error rate (BER) performance of MIMO-OFDM eigenmode transmission with and without MMSE interference canceller. In the experiment, a time-varying channel is synthetically generated in a static environment by exploiting the inherent spatial correlation in a static environment. Our experimental results proved the robustness of MIMO-OFDM eigenmode with MMSE interference canceller in the presence of feedback delay

Adaptive MIMO eigenmode transmission system is a promising candidate for future high data rate wireless systems. However under practical conditions when channel state information (CSI) is imperfect, the eigenbeams lose their orthogonality and inter-eigenmode interference occurs. No work so far has attempted to consider the effects of inter-eigenmode interference on the adaptive signaling algorithm which is essential in ensuring a practical and robust adaptive system. Thus in this paper, we will propose an adaptive algorithm that account for CSI imperfections and practical operating conditions explicitly, namely imperfect channel estimation at receiver, delayed quantized feedback to transmitter and a spatially correlated continuous fading channel. A metric for the SINR of each eigenmode under the above practical conditions is identified and this metric is used in the adaptive signaling to ensure a robust adaptive algorithm. Both simulation and experimental results showed that the proposed algorithm is robust and superior to conventional schemes under practical operating conditions. Furthermore, a low complexity look up table-based computation method is also devised

Adaptive MIMO eigenmode transmission system is a promising candidate for future high data rate wireless systems. However under practical conditions when channel state information (CSI) is imperfect, the eigenbeams lose their orthogonality and inter-eigenmode interference occurs. No work so far has attempted to consider the effects of inter-eigenmode interference on the adaptive signaling algorithm which is essential in ensuring a practical and robust adaptive system. Thus in this paper, we propose an adaptive algorithm that account for CSI imperfections explicitly. Our results showed that the proposed algorithm is robust and superior to conventional schemes under practical operating conditions. Furthermore, a low complexity look-up table-based computation method is also devised.