| This thesis is based on Massey's model on collision channels without feedback, in which collided packets are considered unrecoverable. A collision occurs if two or more packets are partially or totally overlapped. Each potential user is assigned a deterministic zero-one pattern, called the protocol sequence, and sends a packet if and only if it is active and the value of the sequence is equal to one. Due to lack of feedback, the beginning of the protocol sequences cannot be synchronized and variation in relative offsets is inevitable. It further yields variation in throughput.;We study the design of protocol sequences from three different perspectives.;First of all, in order to minimize variation of throughput due to delay offsets, we investigate protocol sequences whose pairwise Hamming cross-correlation is a constant for all possible relative offsets. It can be viewed as a generalization of completely shift-invariant sequences, which can achieve the zero-variation in throughput over a slot-synchronized channel.;The second one is a non-blocking property which ensures that each active user can successfully transmit information at least once in its each active period. With the assumption that all potential users may be active simultaneously, user-irrepressible sequences and completely irrepressible sequences are studied respectively for different level of synchronization, to support the non-blocking property.;Provided that the number of active users is smaller than the number of potential users, strongly conflict-avoiding codes are introduced with the non-blocking property in the asynchronous channel. It can be viewed as an extension of completely irrepressible sequences.;At last, we focus on the detection problem in the protocol sequence design. The objective is to construct user-detectable sequences that allow any active user be detected by the receiver via some algorithm within some bounded delay if and only if it has become active. |
