Transmission Merging Mechanism

3.3.1 Transmission Merging Mechanism

In order to merge the transmission, the first problem is UGS connections which are periodically allocated fixed amount of BW. For UGS connections, the strategy is that using the parameter” maximum latency” adjusts the transmission time. After merging UGS, the latency of the rtPS will be considered to adjust the transmissions time. Finally, the non-real-time services are transmitted along with the real-time services. The major problem of the merging is that how many frames’ traffic can be merged into one frame and doesn’t exceed the frame size. The detail is below.

(1) UGS connections merging

A UGS connection is periodically allocated BW and each UGS would be given a QoS parameter “maximum latency”. If the maximum latency of the connection i of node k is given d_i,k frames, it means the allocation can be delayed d_i,k frames. So according this parameter, we can merge the UGS allocation of node k to reduce the awake-amount of frames.

The algorithm is as Figure 3.5. By this UGS merging algorithm, we can calculate the farthest next awake-frame frame F and the nearest next awake-frame frame Y. In our algorithm, we expect to merge transmissions as much as possible. By Y and F, we can get the adjustment space after UGS merging.

Firstly, it sorts the UGS connections’ transmission frames according Y_i,k and F_i,k which are the next transmission frame, and the farthest transmission frame of the UGS connection i.

A UGS connection’s transmission can be merged if it satisfies the condition F_a≦F , where the Fa is the farthest next awake-frame frame of this connection. When a UGS connection is added into the next UGS transmission frame, the F and Y will be adjusted. The algorithm simple example is shown in the Figure 3.6. The firstly coming transmission is UGS1, and the transmission of both UGS₂ and UGS₃ can be merged with UGS₁. But, after the transmission of UGS2 is merged with UGS1, the transmission of UGS3 will not be merged with transmission of UGS₁ and UGS₂.

Function: Get_Next_UGS Input:

For each UGS connection i of PS mode MSS k

pi,k：UGS Duration(frames), di,k：Max latency(frames), vi,k：BW-allocated Yi,k：The next transmission frame of the UGS i

Fi,k = Yi,k + di,k

There are N UGS connections of i.

Output:

Y：Farthest next awake-frame F：Nearest next awake-frame 1. Sort the N connections according the Y_i,k ,and F_i,k, denoted

Figure 3.5 The algorithm of UGS merging

d₁ d_i= maximum latency

Figure 3.6 The algorithm illustration of UGS merging

The Figure 3.7 shows an example with three UGS connections. The parameters of each connection is shown in Table 3.2. In the example, after UGS merging, we can see the 5^th frame of UGS 3, the 6^th frame of UGS 2, and the 7^th frame of UGS 1 can be merged into 7^th frame. The 9^th frame of UGS 2 and the 10^th frame of UGS 3 can be merged into 10^th frame.

The 14^th frame of UGS 1, the 15^th frame of UGS 2, and the 15^th frame of UGS 2 can be merged into 15^th frame. There is some adjusting space for 3^th frame and 12^th frame. The adjusting space is considered in rtPS merging

Table 3.2 Merging example parameter table Grant Duration(frame) Max Latency(frame)

UGS 1 5 1

Merge 1,2,3 Merge 2,3 Merge 1,2,3 di= maximum latency

Figure 3.7 An example of UGS transmission merging

(2) rtPS connections merging

An uplink rtPS connection is periodically polled by the BS or updates packet information by piggyback. In this system, the BS gets the rtPS queue size by piggyback for PS mode MSS.

If the awake interval is too long, there will be two problems. One is the maximum latency parameter is not be satisfied and the other one is the merging of the rtPS connections maybe exceed the frame size.

For the first problem, as shown in the Figure 3.8, the packets coming between i^th and (i+1)^th awake-frame are known by BS when node uplink data in the (i+1)^th awake-frame by piggyback. These arriving packets must be scheduled in d which is the maximum latency. So, the (i+2)^th awake-frame must be appear in d. In order to satisfying all rtPS of the MSS, we choose the minimum value. So, for the first problem, we can get two formulas：

1. The maximum awake interval is bounded by n1(k)= Min (di,k )-2 for MSS k; and 2. Any three awake-frames must be less than Min (d_i,k ),

where di,k is the delay of the i^th connection for the MSS k

d (Latency)

rtPS Time

i+1 i+2 i

Awake frame

Figure 3.8 The relation between awake-frames and maximum latency of a rtPS connection

For the second problem, we can consider this problem by rtPS and nrtPS’s rmin. We want to find how many frames’ traffic of the MSS can be merged into one frame. Firstly, we calculate the residual capacity by the essential requests of all connections, as shown (3.2).

⎟⎟⎠

Then, we calculate the average BW request of the PS MSS k.

∑

∑

=

k MSS of

rtPS nrtPSofMSSk

k

We can get the maximum awake interval as below.

Avg(k) 1

means how many other frames’ traffic of the PS MSS can be merged into this frame.

In order solving these two problems, we get the maximum awake interval as

The merging algorithm for UGS and rtPS is shown in Figure 3.9. The main idea of the algorithm is to consider the rtPS latency requirement, and the maximum awake interval and to decide the next awake frame with longest sleep interval according to the Y and F. If necessary, it will add extra awake-frame to make it.

Function：Get_Next_Frame Input：

D_k= Min(D_i,k) –minimum value of all rtPS connections’ latency of the MSS k.

D_i,k is the latency of i^th connection of MSS k n - The max awake interval,

Output：

Y - next_awake_frame #

1. Call Get_Next_UGS() to get the Y and F 2. if( (Y≦n) && (Y≦Dk) )

Compare the Yand F with next UGS frame, and choose better one Output Yor F

else

Output F = Min(Dk,-1, n );

Figure 3.9 The algorithm of UGS merging considering rtPS connections

Figure 3.10 is the example after adding the rtPS connection. The minimum latency of all rtPS connection “d” is 7 frames and the maximum awake interval “n” is 3. So, it needs to add awake-frame at the 6 ^th frame

Figure 3.10 An example of transmission merging considering rtPS connections

(3) nrtPS and BE connections merging

Because the nrtPS and BE connections are non-real time, the latency requirement is not considered, and we also consider the minimum reserved rate of nrtPS when calculating the maximum sleep interval. So the nrtPS and BE are transmitted with the rtPS and UGS connections.