I know this is not the community to discuss my homework problem but I cam confused because I cannot find a formula that can find data rate for 802.11g standard given modulation, coding rate and transport layer protocol. And how does transport layer affect the data rate of 802.11g?
The transport layer does not affect the data rate of 802.11 networks.
The data rate is the the rate at which the AP and client modulate frames. This is based on the signal-to-noise ratio (SNR) between the AP and the wireless client. This is highly variable based on many conditions, including RF interference, distance, device drivers, etc. and often fluctuates over time.
Throughput is what we can measure within the TCP/IP stack, which is where our transport layer comes into play. This is also highly variable depending on quite a few factors, such as:
- application protocol
- backhaul (how the AP is connected to the wired network)
- wireless data rate
- other wireless clients in the cell
- RF interference
You can make educated guesses by taking the data rate (say, 54Mbps) and dividing it by two (because Wi-Fi is a half-duplex medium), then using that as a line rate for further calculations that take into account the overhead of your protocol.
For 802.11g data rates, I would refer to this article: https://en.wikipedia.org/wiki/IEEE_802.11g-2003#Technical_description
Modern wireless protocols (802.11n and newer) use Modulation Coding Scheme (MCS) to determine the data rate. There's a great table at http://mcsindex.com that shows all the data rate combinations for MCS.