Sign-Compute-Resolve for Random Access

We present an approach to random access that is based on three elements: physical-layer network coding, signature codes and tree splitting. Upon occurrence of a collision, physical-layer network coding enables the receiver to decode the sum of the information that was transmitted by the individual users. For each user this information consists of the data that the user wants to communicate as well as the user's signature. As long as no more than $K$ users collide, their identities can be recovered from the sum of their signatures. A splitting protocol is used to deal with the case that more than $K$ users collide. We measure the performance of the proposed method in terms of user resolution rate as well as overall throughput of the system. The results show that our approach significantly increases the performance of the system even compared to coded random access, where collisions are not wasted, but are reused in successive interference cancellation.Comment: Accepted for presentation at 52nd Annual Allerton Conference on Communication, Control, and Computin

Sign-Compute-Resolve for Tree Splitting Random Access

We present a framework for random access that is based on three elements: physical-layer network coding (PLNC), signature codes and tree splitting. In presence of a collision, physical-layer network coding enables the receiver to decode, i.e. compute, the sum of the packets that were transmitted by the individual users. For each user, the packet consists of the user's signature, as well as the data that the user wants to communicate. As long as no more than K users collide, their identities can be recovered from the sum of their signatures. This framework for creating and transmitting packets can be used as a fundamental building block in random access algorithms, since it helps to deal efficiently with the uncertainty of the set of contending terminals. In this paper we show how to apply the framework in conjunction with a tree-splitting algorithm, which is required to deal with the case that more than K users collide. We demonstrate that our approach achieves throughput that tends to 1 rapidly as K increases. We also present results on net data-rate of the system, showing the impact of the overheads of the constituent elements of the proposed protocol. We compare the performance of our scheme with an upper bound that is obtained under the assumption that the active users are a priori known. Also, we consider an upper bound on the net data-rate for any PLNC based strategy in which one linear equation per slot is decoded. We show that already at modest packet lengths, the net data-rate of our scheme becomes close to the second upper bound, i.e. the overhead of the contention resolution algorithm and the signature codes vanishes.Comment: This is an extended version of arXiv:1409.6902. Accepted for publication in the IEEE Transactions on Information Theor

A random access scheme with physical-layer network coding and user identification

A slotted random access scheme is proposed that is based on physical-layer network coding. The scheme uses signature codes that enable the receiver to detect which users are active in each round and which linear combination of pckets is received. Feedback enables in each round, one of the users to drop a packet, keeping the queue sizes lmited. It is proven that for a broad class of feedback mechanisms the scheme is stable in the sense that the receiver can eventually decode all packets. Numerical results demonstrate that the scheme performs well in terms of the expected queue size, the maximum delay as well as the expected number of retransmissions per packet

A random access scheme with physical-layer network coding and user identification

A slotted random access scheme is proposed that is based on physical-layer network coding. The scheme uses signature codes that enable the receiver to detect which users are active in each round and which linear combination of pckets is received. Feedback enables in each round, one of the users to drop a packet, keeping the queue sizes lmited. It is proven that for a broad class of feedback mechanisms the scheme is stable in the sense that the receiver can eventually decode all packets. Numerical results demonstrate that the scheme performs well in terms of the expected queue size, the maximum delay as well as the expected number of retransmissions per packet