Distributed Double-Differential Modulation for Cooperative Communications Under CFO

Abstract

When a terminal is recruited to cooperate with other neighboring terminals, its channel state and carrier frequency offset (CFO) may be unknown to the destination. Under these circumstances, this paper considers the use of distributed double-differential (DD) modulation, which simplifies receiver implementation because it by-passes channel and CFO estimation. Two double-differential codecs are proposed transmitting: i) across orthogonal channels using time-division multiplexing, achieving rate and error performance similar to that of co-located multi-antenna DD systems; or ii) simultaneously, benefiting from the distinct CFOs across terminals and bypassing the need of ordering protocols. Both (i)-(ii) approaches are considered in adaptive-and selective-relaying cooperation protocols demonstrating that maximum spatial diversity is achievable. Simulations corroborate the theoretical error performance claims.

Distributed Double-Differential Orthogonal Space-Time Coding for Cooperative Networks

“…It can be seen from Fig. 3 that the proposed distributed DD coding outperforms the same rate conventional scheme [11] at all SNRs. For example, a gain of 5 dB is achieved at SER=10 −4 .…”

“…Proposed Scheme versus Distributed DD Code of [11] In Fig. 3, we have implemented the proposed distributed DD code and the conventional distributed DD code [11] by assuming that the channel between the source and the relays is perfect and noise free.…”

“…3, we have implemented the proposed distributed DD code and the conventional distributed DD code [11] by assuming that the channel between the source and the relays is perfect and noise free. The distributed DD code of [11] uses the time-division multiplexing (TDM) transmission strategy suggested in [11,Section III]. It can be seen from Fig.…”

“…It requires previous source discoveries and a complicated ordering protocol such that each relay can know its transmission time accurately. A simultaneous transmission strategy is also proposed in [11] in order to avoid the ordering of the relays. However, this scheme requires that the channel remains constant over more than 10 4 time-intervals.…”

“…was proposed in [10], however, it can only be applied to a specific class of space-time block code (STBC), which belongs to the diagonal unitary group. A time-division multiplexed (TDM) distributed DD coding based on [10] for cooperative systems is proposed in [11]. This scheme uses regenerative relays for transmission of a diagonal double-differentially encoded matrix.…”