Ibrahim Altunbas

Cooperative Diversity for Intervehicular Communication: Performance Analysis and Optimization

Although there has been a growing literature on cooperative diversity, the current literature is mainly limited to the Rayleigh fading channel model, which typically assumes a wireless communication scenario with a stationary base station antenna above rooftop level and a mobile station at street level. In this paper, we investigate cooperative diversity for intervehicular communication based on cascaded Nakagami fading. This channel model provides a realistic description of an intervehicular channel where two or more independent Nakagami fading processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. We investigate the performance of amplify-and-forward relaying for an intervehicular cooperative scheme assisted by either a roadside access point or another vehicle that acts as a relay. Our diversity analysis reveals that the cooperative scheme is able to extract the full distributed spatial diversity. We further formulate a power-allocation problem for the considered scheme to optimize the power allocated to the broadcasting and relaying phases. Performance gains up to 3 dB are obtained through optimum power allocation, depending on the relay location.

Design of serial concatenated MSK schemes based on density evolution

We consider the design of convolutional codes and low density parity check (LDPC) codes with minimum-shift keying (MSK) when the receiver employs iterative decoding and demodulation. The main idea proposed is the design of coded schemes that are well matched to the iterative decoding algorithm being used rather than to hypothetical maximum-likelihood decoding. We first show that the design is crucially dependent on whether the continuous phase encoder (CPE) is realized in recursive form or in nonrecursive form. We then consider the design of convolutionally coded systems and low density parity check codes with MSK to obtain near-capacity performance. With convolutional codes, we show that it is possible to improve the performance significantly by using a mixture of recursive and nonrecursive realizations for the CPE. For low density parity check codes, we show that codes designed for binary phase shift keying are optimal for MSK only if the nonrecursive realization is used; for the recursive realization, we design new LDPC codes based on the concept of density evolution. We show that these codes outperform the best known codes for MSK and have lower decoding complexity.

Cooperative Diversity for Relay-Assisted Inter-Vehicular Communication

Although there has been a growing literature on cooperative diversity, the current literature is mainly limited to Rayleigh fading channel model which typically assumes a wireless communication scenario with a stationary base station antenna above roof-top level and a mobile station at street level. In this paper, we investigate cooperative diversity for inter-vehicular communication based on cascaded Rayleigh fading. This channel model provides a realistic description of inter-vehicular channel where two or more independent Rayleigh fading processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. We investigate the performance of amplify-and-forward relaying for an inter-vehicular cooperative scheme assisted by a road-side access point which acts as a relay. Our diversity analysis reveals that the cooperative scheme is able to extract the full distributed spatial diversity. We further formulate a power allocation problem for the considered scheme to optimize the power allocated to broadcasting and relaying phases. Performance gains up to 2.8 dB are observed through optimum power allocation depending on the relay location.

Performance of space-time block codes with transmit antenna selection in Nakagami-m fading channels

In this paper, multiple-input multiple-output (MIMO) systems employing orthogonal space-time block codes (STBCs) with transmit antenna selection (TAS) are examined for uncorrelated flat Nakagami-m fading channels. Exact symbol error rate (SER) expressions for M-ary modulation techniques are derived by using the moment generating function (MGF)-based analysis method. In the SER analysis, the receiver antennas are assumed to use maximal ratio combining (MRC) whereas a subset of transmit antennas that maximizes the instantaneous received signal-to-noise ratio (SNR) is selected for STBC transmission. The derived SER results for different numbers of receive and transmit antennas are validated by Monte Carlo simulations and it is shown that the investigated systems achieve full diversity orders at high SNRs.

On the design of LDPC codes for MSK

We investigate serial concatenation of low-density parity check (LDPC) codes and minimum shift keying (MSK) with iterative decoding. We show that the design of LDPC codes is crucially dependent on the realization of the MSK modulator. For MSK modulators with nonrecursive continuous phase encoders (CPEs), optimal codes for BPSK are optimal, whereas for MSK modulators with recursive CPEs, the BPSK codes are not optimal. We show that for nonrecursive CPEs, iterative demodulation and decoding is not required even though the CPE has memory. However, iterative demodulation is essential for recursive CPEs. For recursive CPEs, we design LDPC codes using density evolution and differential evolution considering iterative demodulation and decoding. The resulting codes provide significantly improved performance over the existing codes.

Performance Analysis of Space-Time Block Codes with Transmit Antenna Selection in Nakagami- m Fading Channels

In this paper, multiple-input multiple-output systems employing space-time block codes (STBCs) with transmit antenna selection (TAS) are examined for flat Nakagami-m fading channels. Exact symbol error rate (SER) expressions for M-ary modulation techniques are derived by using the moment generating function based analysis method. In the SER analysis, the receiver is assumed to use maximal ratio combining whereas a subset of transmit antennas that maximizes the instantaneous received signal-to-noise ratio (SNR) is selected for STBC transmission. The analytical SER results are validated by Monte Carlo simulations. By deriving upper and lower bounds for SER expressions, it is shown that TAS/STBC schemes achieve full diversity orders at high SNRs.

Source Transmit Antenna Selection for Space Shift Keying With Cooperative Relays

In this letter, we propose a cooperative multiple-input multiple-output (MIMO) scheme combining transmit antenna selection (TAS) and space shift keying (SSK). In this scheme, source transmit antennas are selected and SSK is applied by using the selected antennas. Besides the direct link transmission, the relays, that decode the source signal correctly, take part in the transmission. Exact expressions and a considerably accurate approximate expression for the symbol error rate of the proposed SSK system are derived. It is shown that the proposed scheme outperforms the SSK system without TAS and also the conventional cooperative MIMO system, which employs source TAS, at practical signal-to-noise ratio values for especially high data rates and sufficient number of receive antennas at the destination.

Moment generating function-based performance evaluation of amplify-andforward relaying in n¿nakagami fading channels

In this study, the authors investigate the error rate performance of amplify-and-forward relaying over N*Nakagami fading channels. This is a recently introduced channel model that involves the product of N Nakagami-m-distributed random variables. Employing the moment generating function approach, the authors derive symbol error rate expressions for a single-relay system under instantaneous power scaling (IPS) and average power scaling (APS) factors at the relay node, that is, variable and fixed gains. The results achieved by the authors demonstrate that the achievable diversity order is a function of Nakagami fading parameter (m) and degree of cascading (N). An identical diversity order is obtained under both scaling factors when the relay is close to the destination. When the relay is close to the source, IPS becomes advantageous over APS. Monte–Carlo simulations are further provided to confirm the analytical results.

Optimized Amplify-and-Forward Relaying for Vehicular Ad-Hoc Networks

Cooperative communication techniques promise the advantages of MIMO (multi-input multi-output) communications for wireless scenarios with single-antenna terminals. In this paper, we investigate the performance of a vehicle-to-vehicle cooperative scheme where another vehicle in the vicinity of the source vehicle acts as a relay. The underlying source-to-relay, relay-to-destination, and source-to-destination links are modeled as cascaded (double) Rayleigh fading. This statistical model provides a realistic description of inter-vehicular channel where two or more independent Rayleigh fading processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. We derive a pairwise error probability (PEP) expression for the inter-vehicular cooperative scheme under consideration and show that the full distributed spatial diversity is extracted. Based on the derived PEP expressions, we obtain union bounds on the bit error rate performance which are then minimized to optimally allocate power between broadcasting and relaying phases. Optimum power allocation brings performance gains up to 3dB depending on the relay location and deployed modulation scheme.

A Tutorial on Network Coded Cooperation

Network Coding (NC) can significantly help increase the efficient use of network resources. However, directly applying NC to wireless networks is not an effective design solution. Wireless channels are prone to bit errors due to fading, possibly generating erroneous decisions at the relay nodes while applying NC. Furthermore, the broadcast nature of wireless channels may provide a direct communication link between source and destination nodes. In order to combat fading channel impairments, and also to exploit the inherent spatial diversity provided through the direct link, network coded cooperation (NCC) techniques should be incorporated to the NC systems for wireless networks. This tutorial provides an overview of the state-of-the-art in the NCC systems, combining the powerful tools of NC and cooperative communication, in order to increase data transmission rates and robustness of multiple source wireless networks.