Chpater 3 Proposed MAC Protocol
3.4 The proposed protocol
In this section, we introduce how our protocol works. A node i which intends to transmit data to a receiver j checks its Noisethresh,, and then checks its neighbor table.
Node i nearby has m ongoing transmission nodes, and the node j nearby has n ongoing transmission nodes. If the Noisethresh can be met, a node i will calculate a power PRTS to transmit RTS. Otherwise, node i remains silent and keeps monitoring the channel status. PRTS is a maximum allowable power for a node to transmit RTS without disrupting its nearby transmissions. We can calculate a power PRTS by equation 1 and equation2.
15 In the equation 1, Ps is a free space receiving signal strength of i’s nearby ongoing transmission node k from the sender i. G( i, k ) is an antenna gain between the sender i and its neighbor k. d( i, k ) is the distance between the sender and its nearby ongoing transmission node k. α is the constant with range 2 to 4. C is a constant depends on the environment..
In the equation 2, Sn(k) is a receiving data signal strength of nearby ongoing transmission node k. Nr(k) is a noise of nearby ongoing transmission node k.
SNRthresh(k) is a threshold for nearby ongoing transmission node k to decode data correctly. In the equation 2, we regard it Ps(k) the additional noise to other nearby transmission nodes k. The additional noise can’t affect every nearby ongoing transmission node k. Every node k’s SNR must above its threshold. By combining equation 1 and 2, we can get the equation 3.
RTS
The sender i also adds its noise information Nr into RTS. If collisions happen or the sender i can’t overhear CTS in a period, sender i will retransmission RTS by Pr which we will introduce in the section 3.6. After the intended receiver j receives RTS, it can calculate its channel gain G(i,j) between the sender i. The intended receiver can also
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calculate a power Pmin for the sender i to transmit data, and the receiver j use PCTS to transmit CTS message. PCTS must satisfy the following two conditions. First, the maximum allowable power for a node to transmit CTS can’t disrupt receiver nearby transmissions. We can calculate it by equation 4 and 5.
= α
In the equation 4, Pr(k)is a free space receiving signal strength of j’s nearby ongoing transmission node k from the receiver j.
) transmission nodes k. The additional noise can’t affect every nearby ongoing transmission node k. Every node k’s SNR must above its threshold. By combining equation 4 and 5, we can get the equation 6.
CTS
Second, the sender can successfully decode CTS. We can calculate it by equation 7 and 8.
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In the equation 7, P is a free space receiving signal strength of the sender i from the i receiver j.
In the equation 8, the sender i’s receive signal strength is P , and the receive signal i to noise ratio of sender i must above its SNR threshold.
The intended receiver also set one to a fag, and add Pmin, Nr(j), Sn, flag and SNRthreshold into CTS. Pmin is a power that doesn’t distribute ongoing transmition and it is greater than SNR threshold for receivers to decode. Pmin also must satisfy the following two conditions. First, the sender transmitting data can’t disrupt any ongoing transmissions. We can calculate it by equation 9 and equation 10.
= α
In the equation 9, Ps(k)is a free space receiving signal strength of i’s nearby ongoing transmission node k from the sender i.
)
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In the equation 10, we regard Ps(k) as the additional noise to other nearby transmission nodes k. The additional noise can’t affect every nearby ongoing transmission node k. Every node k’s SNR must above its threshold. By combining equation 9 and 10, we can get the equation 3.
min
Second, Pmin must greater than threshold for the receiver to decode correctly. We can calculate it by equation12 and 13.
= α
In the equation 11, Pj is a free space receiving signal strength of the sender i from the receiver j.
In the equation 13, the receiver j’s receive signal strength is Pj , and the receive signal to noise ratio of receiver j must above its SNR threshold.
Then receiver’s neighbors overhear CTS update their neighbor tables. They check a
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flag of CTS, if a flag is equal to one, they relay CTS, and set flag zero. After the sender i receives CTS, it transmits data using a instructed power Pmin according to the information in CTS. When the sender i finish transmitting data, it adds PACK
information into a tail of data frames. PACK must satisfy the following two conditions.
First, a maximum allowable power for a node to transmit ACK cannot disrupt nearby ongoing transmissions. We can calculate it by equation 14 and 15.
= α
In the equation 13, Pr(k)is a free space receiving signal strength of j’s nearby ongoing transmission node k from the receiver j.
) additional noise can’t affect every nearby ongoing transmission node k. Every node k’s SNR must above its threshold. By combining equation 14 and 15, we can get the equation 16.
Second, the sender can successfully decode CTS. We can calculate it by equation 17 and 18.
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In the equation 7, P is a free space receiving signal strength of the sender i from the i receiver j.
In the equation 17, the sender i’s receive signal strength is P , and the receive signal i to noise ratio of sender i must above its SNR threshold. After the transmission finish, node i and node j’s neighbors update their neighbor tables to change the transmission state from an ongoing transmission state to an idle state.
Here we show the example of our protocol. As shown in Fig. 3-1. ,node A wants to transmit Data to node B. Node A first checks its neighbor table to calculate a power PRTS to transmit a RTS. When node B receives RTS, it computes a channel gain by receiving RTS signal strngth between a node A and node B, and node B can also calculate a power Pmin for a sender to transmit data, and encapsulates power information Pmin and noise information into CTS and then return a CTS to node A with PCTS. When node B’s neighbors overhear a CTS, they update their neighbor table to change a transmission state from an idle state to an ongoing transmission state and determinate whether to help relaying a CTS. In Fig. 3-2., node A uses Pmin to transmit data to node B. In Fig. 3-3., aftert fisnishing transmitting data, node A calculates a power PACK for node B to transmit ACK . The power information PACK added at a tail of data. Node B uses power PACK to transmit ACK .In Fig. 3-4. and Fig. 3-5., node
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A is transmitting data to node B, and node C wants to transmit data to node D. Node C first checks its neighbor table( find node B is receiving data), and it uses a power PRTS to tansmit RTS . Node D uses power PCTS to transmit CTS , and node C uses Pmin to transmit data. Finally, node D uses PACK to transmit ACK. Fig. 3-6. shows a basic operation of our protocol. Fig. 3-7. is the flow chart of our protocol.
Figure 3 - 1 Example of our protocol (1)
Figure 3 - 2 Example of our protocol (2) .
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Figure 3 - 3 Example of our protocol (3)
Figure 3 - 4 Example of our protocol (4)
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Figure 3 - 5 Example of our protocol (5)
Figure 3 - 6 The basic operation of the protocol
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Figure 3 - 7 The flow chart of our protocol