Embracing Interference in Ad Hoc Networks Using Joint Routing and Scheduling with Multiple Packet Reception

We present an approach that takes advantage of multi-packet reception (MPR) to reduce the negative effects of multiple access interference and therefore increase the capacity of an ad hoc network. We analyze the performance upper bound of joint routing and scheduling for ad hoc networks that embrace interference by using MPR. We formulate the optimization problem under a deterministic model and seek to maximize the aggregate network throughput subject to minimum rate requirements. We then propose a polynomial-time heuristic algorithm aimed at approximating the optimal solution to the joint routing and channel access problem under MPR. We show the effectiveness of our heuristic algorithm by comparing its performance with the upper bound.

In this paper, the performance of a binary phase shift keyed random\ntime-hopping impulse radio system with pulse-based polarity randomization is\nanalyzed. Transmission over frequency-selective channels is considered and the\neffects of inter-frame interference and multiple access interference on the\nperformance of a generic Rake receiver are investigated for both synchronous\nand asynchronous systems. Closed form (approximate) expressions for the\nprobability of error that are valid for various Rake combining schemes are\nderived. The asynchronous system is modelled as a chip-synchronous system with\nuniformly distributed timing jitter for the transmitted pulses of interfering\nusers. This model allows the analytical technique developed for the synchronous\ncase to be extended to the asynchronous case. An approximate closed-form\nexpression for the probability of bit error, expressed in terms of the\nautocorrelation function of the transmitted pulse, is derived for the\nasynchronous case. Then, transmission over an additive white Gaussian noise\nchannel is studied as a special case, and the effects of multiple-access\ninterference is investigated for both synchronous and asynchronous systems. The\nanalysis shows that the chip-synchronous assumption can result in\nover-estimating the error probability, and the degree of over-estimation mainly\ndepends on the autocorrelation function of the ultra-wideband pulse and the\nsignal-to-interference-plus-noise-ratio of the system. Simulations studies\nsupport the approximate analysis.\n

Multi-Packet Reception (MPR) enables simultaneous receptions from different transmitters to a single receiver, which has been demonstrated to bring capacity improvement in wireless network. However, MPR does not improve the transmission capability of intermediate relay nodes in a multi-hop routing and thus these nodes may become the bottlenecks for increasing throughput despite of great reception capability. We investigate the scheduling for multi-hop routing with MPR to improve the network throughput under multiple data flows. We formulate the optimization problem under K-MPR model and analyze the performance upper bound with ideal scheduling. We propose a distributed scheduling scheme based on a k-Connected k-Dominating Set backbone to eliminate bottleneck effects on intermediate relay nodes as to enhance the network throughput. We show the effectiveness of our scheme by comparing its performance with the upper bound and node-disjoint routing.

Multiple packet reception (MPR) is becoming a viable reality for wireless random access protocols thanks to advances in the physical layer and new coding techniques. In the simplest $K$ -MPR model, a receiver can resolve up to $K\geq 1$ parallel transmissions. We extend the classical analysis of pure and slotted ALOHA to $K$ -MPR devices with arbitrary degree $K$ for fixed and variable packet size. Through a parsimonious modeling approach, we derive relatively simple analytical expressions. In this way, we gain insight and quantitative understanding on the fundamental tradeoffs between pure and slotted ALOHA and on the scaling of maximum achievable throughput with $K$ .

Recent advances in interference cancellation and signal-processing techniques can enable full-duplex radios and multipacket reception (MPR), which will have significant impact on medium access control (MAC) schemes. In this paper, we propose a MAC scheme in unmanned aerial vehicle (UAV) ad-hoc networks with full-duplex radios and MPR. To efficiently handle the highly mobile environment of a UAV ad-hoc network, a token-based technique is used to update information in the network as well. The MAC schemes in the presence of perfect and imperfect channel state information (CSI) are formulated as a combinatorial optimization problem and a discrete stochastic optimization problem, respectively. Simulation results show the effectiveness of the proposed MAC.

We present packet switching applications based on extended spectral-amplitude-coding (SAC) labels in generalized multi-protocol label switching (GMPLS) networks. The proposed approach combines the advantages of wavelength-division multiplexing (WDM) and optical code-division multiple access (OCDMA). The extended SAC labels preserve the orthogonal property to avoid the effect of multiple access interference (MAI) shown at the decoder. We investigate the node architecture of label generation/recognition based on arrayed waveguide grating (AWG). Combining cyclic-shifted maximal length sequence (MLS) codes with the wavelength routed property of AWG simplifies the node structure. The simulation results show that the proposed labels achieve good performances against receiver noise due to the low average cross-correlation values. Under a given bit-error-rate (BER), the switching efficiency of the extended SAC labels outperforms the previous OCDMA schemes, as the network nodes are capable of processing a large number of labels simultaneously.

This paper presents an investigation into improving the channel estimation scheme and reducing the effects of symbol timing misalignment when the digital video broadcasting-return channel through terrestrial (DVB-RCT) is used as return path model. Under orthogonal frequency division multiple access (OFDMA) which uses the modulation scheme of DVB-RCT, appropriate symbol length of constant-amplitude zero-autocorrelation (CAZAC) sequences as a preamble could be utilized in accordance with the number of transmitting antenna and channel condition. However, because its capability of channel estimation is limited by the number of transmitting antennas and multipath components to maintain the orthogonality, we propose more flexible preamble design called extended-CAZAC (E-CAZAC). Also, taking into account the effect of multiple access interference (MAI) introduced by a symbol timing misalignment, the bit error rate (BER) and throughput performance are investigated for a typical OFDMA uplink scenario.

This paper aims to compare the performance of the different transmit signal design techniques that have been proposed recently for DL MC-CDMA systems and presents a joint space-frequency multi-user pre-filtering and spreading scheme. We consider the use of antenna arrays at the base station (BS) and a single antenna at the mobile terminal (MT) and derive the proposed multi-user space-frequency pre-filtering technique that formats the transmitted signals to eliminate the effects of multiple access interference (MAI) and channel distortions at the mobile terminals, whilst maintaining low MT complexity. Thus, two types of detectors are considered at the MT: simple despreading and single user equalizers. The performance of the different schemes is evaluated, considering either perfect or non-perfect CSI and channel coding based on UMTS specifications, in order to select the best strategy for DL TDD MC-CDMA systems.

In this paper, we investigate the impact of modulation index on the performances of SCM SAC-OCDMA system. Knowing that zero cross-correlation (ZCC) codes remove the effect of multiple access interference and of phase-induced intensity noise, SCM SAC-OCDM has been investigated using ZCC codes with two types of direct detection, one and all wavelengths of the code. In this hybrid system, the SNR depends on the modulation index for a given effective power of broadband source. In order to maximize the SNR, the optimum values of the modulation index, for different number of subcarriers, are determined analytically for two types of detection. The performance of the optimized system is evaluated based up on BER. The obtained numerical results show that, by optimizing the modulation index, the number of subcarriers (number of active users per ZCC code) is increased and the performance is significantly improved.

Novel closed form formulae of iterative optimal power control and allocation, and criterion for optimal subcarrier allocation are derived for downlink of multicarrier non-orthogonal multiple access (MC-NOMA) systems. For the first time, we present closed form water-filling formulae that quantify exactly the following effects of multiple access interference for optimal power allocation of MC-NOMA downlink: (i) Each user should take into account the sum of interference from other stronger users plus the receiver Gaussian noise as an equivalent interference in each subcarrier; (ii) The sum of each user’s interference to other weaker users should be accounted as factors which determine the distinct water levels in each subcarrier of each of the other weaker users. We also propose novel iterative water-filling algorithm and projected conjugate gradient algorithm that facilitate iterative computation of optimal power allocation for MC-NOMA downlink.

In this contribution, we consider the performance of multiple-input multiple-output (MIMO) code division multiple access (CDMA) system for digital image transmission over correlated Rayleigh fading channel. MIMO system employs multiple antennas both at the transmitter and receiver. In our work, we consider turbo coded system to investigate the performance of MIMO-CDMA system. We realize turbo code using parallel concatenated convolutional encoder and second convolutional encoder is preceded by random interleaver. Further the output of two convolutional encoder are punctured to get rate of ½. At the receiver, we employ iterative decoding algorithm to reduce the effect of multiple access interference (MAI) and Inter-Symbol-Interference (ISI) and median filters to reduce the effect of salt and pepper noise.. In particular, we evaluate the performance of coded MIMO-CDMA system using Zero forcing (ZF) - multi-user detection (MUD) and minimum mean square error (MMSE)-MUD detection technique to mitigate the effects of multi-stream interference (MSI). It is shown through the simulation study that our considered coded MIMO-CDMA system with MMSE algorithm achieves better picture quality with less signal-to-noise ratio (SNR) as compared to ZF MUD.

In this study, the authors consider the effect of multiple access interference (MAI) on the performance of a quasi‐synchronous multicarrier direct‐sequence code‐division multiple access (QS‐MC‐DS‐CDMA) system. An analytical expression of the bit error rate (BER) is derived for a QS‐MC‐DS‐CDMA system over additive white Gaussian noise channel. The BER performance degradation is proportional to the squares of the even correlation function (ECF) and odd correlation function (OCF) of the spreading codes. The obtained results show that the adequate spreading code is a set of binary zero correlation zone sequences with both zero ECF and OCF. The construction of the latter codes remains a challenge for researchers in the field of code design.

In this paper, a novel direct sequence/spread spectrum (DS/SS) communication system is proposed. This scheme exploits the two-dimensional complex valued chaotic Ikeda map as the spreading sequences. With this double spreading DS/SS system, the effect of multiple access interference can be mitigated by choosing the spreading sequences with appropriate cross-correlation properties. The performance of the system is assessed and demonstrated in a multiuser environment by means of computer simulation with additive white Gaussian noise, Rayleigh fading, and selective fading channel conditions. These studies reveal that the proposed system significantly outperforms the Gold code DS/SS-BPSK system in synchronous channel conditions. In asynchronous case, the improvement is substantial for low signal-to-noise ratios.

We present the performance comparison of delay transmit diversity (DTD), orthogonal transmit diversity (OTD) and space time spreading (STS) schemes in the downlink multicell CDMA systems. The performance was analyzed using the RAKE receiver and the decorrelating receiver under multiuser and multipath conditions. The analysis highlights the effect of multiple access interference on the performance of the system. We derive the instantaneous signal to interference and noise ratio (SINR) for all three schemes using both RAKE and decorrelating receivers. A numerical study is performed to compare the bit error rate (BER) performance of these schemes. We observe that the STS scheme outperforms the other two schemes irrespective of the type of receivers used.

The use of smart or adaptive array antennas has attracted considerable interest in the mobile communications community. We investigate the combined use of an adaptive/smart array antenna and Rake receiver (space-time processing) to jointly mitigate the effect of multiple access interference (MAI) and multipath fading in a CDMA system, while taking angle spread into account. We provide simulation results concerning mean bit error rate (BER) performance of such a system for different numbers of antenna elements, numbers of users and angle spreads. The obtained results show that the investigated smart antenna system can effectively combat adverse MAI and fading effects and improve the CDMA system performance.