Decode-and-forward relaying based on orthogonal complementary codes

In this note, we propose a full-duplex decode-and-forward cooperative diversity scheme based on code division with orthogonal complementary codes. We consider a simple case in which a single user is assisted by a single relay to achieve cooperative diversity. When the cooperation is full-duplex, the operational delay of the relay makes the channel asynchronous and this may cause multiple-access interference (MAI) between the user and relay. The orthogonal complementary codes have perfect autocorrelation and cross-correlation properties that provide MAI-free operation in asynchronous channels. In the proposed scheme, the user and relay terminals spread their messages with complementary codes and the spread messages can reach the destination without interfering with each other. The numerical results reveal that the proposed scheme reaches the same bit-error-rate performance in both synchronous and asynchronous channels. The results are also compared with the conventional orthogonal code sets, such as Hadamard sets, which fail to provide diversity.

Anahtar Kelimeler:

Decode-and-forward relaying, orthogonal complementary codes, CDMA, in-band relays

Decode-and-forward relaying based on orthogonal complementary codes

Keywords:

Decode-and-forward relaying, orthogonal complementary codes, CDMA, in-band relays,

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work in multiuser scenarios. The only limitation in the multiuser case is the number of available complementary codes, which are less than the traditional code sets.
In full-duplex relaying, both uplink and downlink channels are asynchronous due to the processing delay at the relay. The proposed scheme can be applied to both uplink and downlink channels. For half-duplex relaying, considering the asynchronous nature of uplink channel in CDMA networks, the proposed scheme can help to achieve cooperative diversity in the uplink with less overhead.
In this work, we have set the processing delay of relay to a single chip duration. However, any delay including fractional chip durations will not affect the perfect ACF and CCF properties of the complementary codes [10]. In the proposed scheme, the delay introduced by the relay should be estimated at the receiver, which is the only requirement of the system.
The discussion has been kept limited to flat fading channels and the extension to multipath fading channels is left as a future work. It is known that complementary codes keep their properties in multipath fading channels with an adaptive recursive multipath signal reception filter [19].
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