Calculate throughput expressed in terms of useful data bits

Reference no: EM131920637

Question: A mobile phone communicates to a base station (BS) of a cellular system through a dedicated wireless link having the following characteristics:

- The data channel has a constant bit error probability of P_bit= 5 10^-4.

- Each link layer PDU has a size of L = 366 bits, including data, LD = 350 bits, and header, LO = 16 bits, fields.

- The round-trip time at the data link layer - the time taken between the beginning of the transmission of a PDU and the complete reception of the related ACK message, is RTT = 200 ms. tA and propagation delay τp are negligible.

- Link layer PDUs are transmitted at the constant rate Rb = 256 kbit/s.

a) Calculate the throughput expressed in terms of useful data bits transmitted per second for SW-ARQ and SR-ARQ. Why is SW-ARQ so inefficient?

b) Now, consider the following hybrid ARQ (HARQ) scheme. Each PDU is split into K = 6 data blocks of the same size and prior to its transmission is sent to an encoder, which returns an encoded PDU of N data blocks. Encoded PDUs are thus sent over the channel using SR-ARQ. At the receiver, up toN - K erroneous blocks of data can be corrected, in any order, for any PDU. Thus, if a PDU is received with a number of erroneous blocks smaller than or equal to N - K, the corresponding original K-block PDU is recovered with no need for further retransmissions. Otherwise, the PDU is deemed to be failed and a negative acknowledgment is sent to the transmitter, requesting the retransmission of this PDU (of the corresponding N blocks of data). Calculate the throughput (useful data bits per second) of this HARQ scheme for N = 7 and N = 8 and compare the results with those obtained for SR-ARQ.

c) Consider SR-ARQ and the SR-HARQ of the previous point. Let Pf (ARQ) and Pf (HARQ) be the error probabilities for a plain link layer PDU (ARQ) and an encoded PDU (HARQ), respectively. Define Ps(ARQ) = 1 - Pf (ARQ) and Ps(HARQ) = 1 - Pf (HARQ). Referring to ηSR-ARQ and ηSR-HARQ as the throughput of ARQ and HARQ, respectively, say when the following inequality ηSR-HARQ > ηSR-ARQ holds as a function of K, N, Ps(ARQ) and Ps(HARQ).

Reference no: EM131920637

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