Aggregated CDMA Crossbar for Network-on-Chip

Code Division Multiple Access (CDMA) is proposed as the physical layer enabler of Network-On-Chip (NoC) interconnects for its prominent features such as fixed latency, guaranteed service, and reduced system complexity. CDMA interconnects have been adopted by the NoC community as it originates in wireless communications where each bit in a CDMA encoded data word is transmitted on a separate channel to avoid interference. However, the wireless interference problem can be efficiently mitigated in on-chip interconnects eliminating the need for replicating the CDMA channel. Moreover, wireless channels are sequential by nature which is not the case in on-chip interconnects where parallel buses are the default communication means. After CDMA was adopted by the NoC community, the same wireless CDMA scheme has been maintained where each data bit is encoded in a separate CDMA channel and the encoding/decoding logic is replicated for data packets. In this work, we present a novel CDMA encoding/decoding scheme called Aggregated CDMA (ACDMA) for NoC interconnects in which all packet bits are encoded in a single CDMA channel, consequently, eliminating the area and energy overheads resulted from replicating the channel encoding/decoding logic. The ACDMA NoC crossbar is synthesized on a 45-nm standard-cell process. Compared to the conventional CDMA NoC crossbars, the presented method achieves 60.5% less area, 55% less power consumption, and 124% more throughput per area ratio.