Mitigating channel estimation error with timing synchronization tradeoff in cooperative communications

Abstract

Channel estimation error and co-channel interference (CCI) problems are among the main causes of performance degradation in wireless networks. In this paper, we investigate the impact of cooperative communications on mitigating the effect of channel estimation error and CCI. Two main performance criteria, namely, the traditional outage probability and the proposed signal-tonoise ratio (SNR) gap ratio, are utilized to characterize such impact. The SNR gap ratio measures the reduction in the SNR due to channel estimation error or CCI. Taking into consideration the channel estimation error, we show that the outage probability is reduced by utilizing cooperative transmission protocols. We also show that cooperative transmission scenarios, in which each cooperating relay forwards its signal over an orthogonal channel, result in lower SNR gap ratio compared to that of the direct transmission. Thus, cooperative transmission schemes are less susceptible to the effect of channel estimation error compared to direct transmission. Moreover, increasing the number of cooperating relays reduces the effect of the channel estimation error more. Timing synchronization error arises in distributed space-time cooperative schemes, in which the cooperating relays are simultaneously transmitting their signals over the same channel. Unlike the channel estimation error, the effect of the timing synchronization error gets worse as the the number of cooperating relays increases. In this work we also study the tradeoff between the timing synchronization error and the channel estimation error, and show their net impact on the system performance. Finally, we illustrate that CCI can be modeled in a similar fashion to the channel estimation error, and hence the cooperative transmission schemes are also less susceptible to the effect of CCI.

Many-to-many space-time network coding for amplify-and-forward cooperative networks: node selection and performance analysis

“…Overlooking the impact of timing synchronization errors could lead to detrimental effects on the network performance [13]. Also, channel state information errors at the receiving nodes are inevitable in practice [14]. Such errors could drastically diminish diversity gains and thus must be carefully characterized.…”

Dispensing with Channel Estimation: Differentially Modulated Cooperative Wireless Communications

“…The above distributed VAA formed via user cooperation naturally leads to a number of new challenges, among others synchronization, channel estimation, appropriate cluster formation as well as resource allocation [42][43][44][45][46][47], some of which will be detailed in this tutorial. In practice, the knowledge of channel state information (CSI) is typically obtained using a channel sounding sequence.…”

Interference Tolerant Based CR System with Imperfect Channel State Information at the CR-Transmitter

“…The accuracy of the feedback or channel measurement is vulnerable to noise, estimation error, and feedback delay, etc. Considering this reality, we assume that the CR-transmitter knows a noisy version of the channel state amplitude   h where  h h  e. Similar to [5] and [6], the additional error term in the estimated channel coefficient, e, and it is modeled as a zero mean complex Gaussian random variable with a variance    . Now, the transmit power allocated to the CR-tx with the imperfect knowledge of CSI can be written as P CR ≤ I pk   h  .…”