Question: The access point (AP) of a wireless system uses TDMA to transmit data packets to the Nu users within coverage. The TDMA frame has Nu access slots, whereas packet arrivals at the AP for each user are Poisson distributed with parameter λ packet/s. The packet transmission time, tP, is constant and equal to the TDMA slot duration. Consider the following two system configurations:
A Incoming packets at the AP are queued in a single queue in the order in which they arrive. At each TDMA slot the head of line (HOL) packet is picked from the queue and transmitted over the channel, whereas no transmission occurs during this slot if the queue is found empty.
B Nu queues are maintained at the AP, one for each user in the system. Each time a packet directed to user i arrives at the AP, it is inserted in the corresponding queue. During slot i, the HOL packet is picked from queue i and transmitted over the channel, in the next slot the HOL packet of queue (i + 1) mod Nu is transmitted and so on, that is, queues are cyclically served, one per TDMA slot. No transmission occurs when a queue is found empty
a) Which of the two configurations above performs better in terms of normalized throughput?
b) Which one provides better performance in terms of average queueing delay?