Superiority of TDMA in a class of Gaussian multiple-access channels with a MIMO-AF-relay

Knabe, Frederic; Mohamed, Omar; Huppert, Carolin

doi:10.1109/iswcs.2012.6328442

Cited by 1 publication

(12 citation statements)

References 7 publications

(21 reference statements)

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“…As it can be seen from the above equations the choice of F only influences the last term inside the logarithm in (3) and (4), while the other terms are constant. However, compared to the optimization problem with absent direct links [4], we have the additional term W, which occurs in the sum-rate but not in the power constraint (2). Hence, the optimal relaying matrix is not the same as in [4].…”

Section: Joint Relaying Schemementioning

confidence: 99%

“…However, compared to the optimization problem with absent direct links [4], we have the additional term W, which occurs in the sum-rate but not in the power constraint (2). Hence, the optimal relaying matrix is not the same as in [4]. As the optimal solution seems to be hard to find, we will derive upper and lower bounds in the following two subsections.…”

Section: Joint Relaying Schemementioning

confidence: 99%

“…However, this structure still contains parameters that are subject to optimization and the optimal solution of this problem remains unknown. For the case of a single receive antenna, the above problem could be solved in [4], where it was also shown that time-division multipleaccess (TDMA) further increases the achievable sum-rate. In [5], a single-user system was considered, where the transmit covariance matrices were fixed to scaled identity matrices.…”

Section: Introductionmentioning

confidence: 99%

“…For this system, we first derive new upper and lower bounds on the achievable sum-rate for the case where all transmitters send their signals jointly. Subsequently, we will extend the TDMA-based transmission scheme introduced in [4] to the case where the direct links are present. An optimal solution for this scheme is achieved by an iterative algorithm.…”

Section: Introductionmentioning

confidence: 99%

“…An optimal solution for this scheme is achieved by an iterative algorithm. Finally, the achievable sum-rates of the TDMA and the "joint relaying" scheme will be compared, where it can be seen that the superiority of TDMA found in [4] does not always persist for the case of non-zero direct links. This paper is structured as follows: In Section II, we introduce the channel model and describe the constraints that have to be fulfilled while optimizing the sum-rate.…”

Section: Introductionmentioning

confidence: 99%

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Achievable sum-rates in Gaussian multiple-access channels with MIMO-AF-relay and direct links

Knabe

Mohamed

Huppert

2012

2012 IEEE Information Theory Workshop

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Abstract-We consider a single-antenna Gaussian multipleaccess channel (MAC) with a multiple-antenna amplify-andforward (AF) relay, where, contrary to many previous works, also the direct links between transmitters and receiver are taken into account. For this channel, we investigate two transmit schemes: Sending and relaying all signals jointly or using a time-division multiple-access (TDMA) structure, where only one transmitter uses the channel at a time. While the optimal relaying matrices and time slot durations are found for the latter scheme, we provide upper and lower bounds on the achievable sum-rate for the former one. These bounds are evaluated by Monte Carlo simulations, where it turns out that they are very close to each other. Moreover, these bounds are compared to the sum-rates achieved by the TDMA scheme. For the asymptotic case of high available transmit power at the relay, an analytic expression is given, which allows to determine the superior scheme. I. INTRODUCTIONIn today's wireless communication systems, the demand for higher data rates and wide-range coverage is steadily growing. To meet these requirements, a high density of base stations is necessary, which entails high costs for installation and maintenance. Another possibility to increase throughput and coverage is the use of relay nodes, which have much lower costs. Relay channels were considered in [1] first, and have drawn more and more research attention in the last decades.Depending on how the signals are processed at the relay, different types of relaying schemes are distinguished. The most common ones are amplify-and-forward (AF, also called nonregenerative relaying) and decode-and-forward (DF, also called regenerative relaying). While in AF, the relay simply amplifies the received signals subject to a power constraint, a complete decoding and re-encoding of the signal is necessary when using DF. As this yields higher costs and larger delays, we will restrict ourselves to AF relaying schemes in this paper.For multiple input multiple output (MIMO) systems with additive white Gaussian noise (AWGN), the main challenge is to find both the covariance matrix at the transmitter and the matrix that maps the relay's input to its outputs, such that the data rate is maximized. The problem becomes even harder to solve, if a relay system with multiple transmitters, also called a multiple-access relay channel (MARC), is considered. This holds especially if the direct links between transmitters and receiver are also taken into account. A solution for this general problem has not been found yet. However, numerous previous works have made considerable progress at least for some simplified versions of the problem:

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Section: Joint Relaying Schemementioning

confidence: 99%