Non-uniform pilot-symbol allocation for closed-loop OFDM

Panah, Ali Yazdan; Nosrat-Makouei, Behrang; Vaughan, Rodney G.

doi:10.1109/twc.2008.070129

Cited by 13 publications

(8 citation statements)

References 28 publications

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“…Nevertheless, we are able to obtain analytic results that show the relation between the feedback gain and the number of subcarriers and pilot tones. Our proposed IterPR scheme is also shown to achieve significant improvements over those proposed in [29] and [30]. Some preliminary results of this paper have been presented in [33] and [34].…”

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confidence: 78%

“…Unfortunately, an efficient solution for such a problem does not yet exist, even for the case without relays [29], [30]. Therefore, even if the optimal SP function can be found explicitly (which is the case here, as shown in Section III-B), an exhaustive search over all possible choices of (D S , D R ) still requires complexity of…”

Section: System Model and Problem Formulationmentioning

confidence: 99%

“…Note that the statistics of the effective SNRs, as given in the right-hand sides of (28) and (29), are difficult to obtain in closed form. However, a deterministic approximation of the expected values can help us gain intuition on the achievable feedback gain.…”

Section: B the Case With Subcarrier Pairingmentioning

confidence: 99%

“…For a given number of pilots, the placement may affect both the channel estimation error and the availability of good subcarrier channels for data transmission. To minimize channel estimation error, pilot tones should be distributed as evenly as possible across subcarriers [26], [27], whereas to increase the efficiency of 0018-9545/$31.00 © 2012 IEEE data transmission, pilot tones should be assigned to subcarriers with bad channel conditions, leaving good subcarriers for data transmission [29], [30]. With channel estimation feedback, the optimal pilot placement scheme can be derived to exploit the tradeoff between these two effects.…”

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confidence: 99%

“…The concept of feedback-aided pilot placement has been examined for noncooperative systems in [29] and [30]. Different from these works, our studies are focused on AF OFDM relay systems, where both SR and RD channels must be estimated at the receiver.…”

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confidence: 99%

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Feedback-Aided Pilot Placement and Subcarrier Pairing for AF OFDM Relay Channels

Sung

Hong

Chao

2013

IEEE Trans. Veh. Technol.

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Abstract-This paper examines the use of channel feedback to adaptively determine pilot placement among subcarriers in amplify-and-forward (AF) orthogonal frequency-division multiplexing (OFDM) relay systems. With feedback of the previous channel estimate, pilot subcarriers at the source and relay can be reassigned to reduce channel estimation error and ensure that good subcarriers are made available for data transmission. The minimum effective signal-to-noise ratio (SNR) among data subcarriers is utilized as the performance metric for the optimization of the pilot locations. The effective SNR is defined as the receive SNR at the destination, taking into consideration the source-to-relay (SR) and relay-to-destination (RD) channels, as well as their respective channel estimation errors. The feedback gain, which is defined as the ratio between the minimum effective SNR achieved with the optimal feedback-aided pilot placement and that achieved with the equal-spaced pilot placement, is used to measure the gains achieved through feedback. In this paper, we first derive an analytic lower bound on the optimal feedback gain and show its rate of increase with respect to the number of subcarriers. These studies are performed for systems both without and with subcarrier pairing (SP) at the relay. Specifically, in systems without SP, the relay forwards each datum on the same subcarrier on which it is received. In systems with SP, the relay is allowed to reassign the subcarriers used to forward the data received from the source. With the goal of maximizing the minimum effective SNR, the optimal SP scheme is shown to be an inverse mapping between the SR and RD subcarriers with respect to their channel gains. Due to the complexity of finding the optimal placement, a suboptimal but efficient algorithm called the iterative pilot relocation (IterPR) scheme is then proposed. The effectiveness of the proposed IterPR schemes is demonstrated through numerical simulations.Index Terms-Channel estimation, feedback, orthogonal frequency-division multiplexing (OFDM), pilot placement, relaying, subcarrier pairing (SP).

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confidence: 78%

Section: System Model and Problem Formulationmentioning

confidence: 99%

Section: B the Case With Subcarrier Pairingmentioning

confidence: 99%

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