Wireless LAN BW calculation for 4 Nodes

Thread Starter

zulfi100

Joined Jun 7, 2012
557
Consider the scenario shown in below, in which there are four wireless nodes, A, B, C, and D. The
radio coverage of the four nodes is shown via the dashed lines; all nodes share the same frequency. When A transmits, it can only be heard/received by B; when B transmits, both A and C can hear/receive from B; when C transmits, both B and D can hear/receive from C; when D transmits, only C can hear/receive from D.
A - - - - - - - - - - B - - - - - - - - - - C - - - - - - - - - - D
Suppose now that each node has an infinite supply of messages that it wants to send to each of the other nodes. If a message’s destination is not an immediate neighbor, then the message must be relayed. For example, if A wants to send to D, a message from A must first be sent to B, which then sends the message to C, which then sends the message to D. Time is slotted, with a message transmission time taking exactly one time slot, e.g., as in slotted Aloha. During a slot, a node can do one of the following: (i) send a message; (ii) receive a message (if exactly one message is being sent to it), (iii) remain silent. As always, if a node hears two or more simultaneous transmissions, a collision occurs and none of the transmitted messages are received successfully. You can assume here that there are no bit-level errors,
and thus if exactly one message is sent, it will be received correctly by those within the transmission radius of the sender.

(a) Suppose that A sends messages to B, and D sends messages to C. What is the combined maximum rate (e.g., in terms of # messages/slot) at which data messages can flow from A to B and from D to C?

It says that:
When A transmits, it can only be heard/received by B
when D transmits, only C can hear/receive from D.

Ans : 2 messages/slot

Please provide some reasoning for this answer.

Zulfi.
 

Thread Starter

zulfi100

Joined Jun 7, 2012
557
Hi,
I have written the assumptions:
When A transmits, it can only be heard/received by B
when D transmits, only C can hear/receive from D.

So both can transmit simultaneously. So 2 message /slot.

Okay now I have provided my reasoning. If its wrong please provide me the correct reason for it.

Zulfi.
 
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