Proposed algorithm method

The proposed method is illustrated in Fig. 4.12 when two processing modes are

Figure 4.11: WiFi transmission rate and WiFi UL ratio.

introduced. First, we consider that UE operates in no DRX mode and decide when to trigger IDC solution. Second, we consider that UE has operated in DRX mode and decide when to close the DRX mode. The details of our proposed scheme are described as follows:

Initial: assume that UE operates in no DRX mode Step 1: Set window size

Set an appropriate window size for measurement, ex. Radio link failure timer T310 is 50ms. We set 30ms as the window size.

Step 2: UE measures WiFi active time and LTE SINR during the window size It can judge that whether the interference from WiFi is serious.

Step 3: Decide the DRX active ratio µ

To ensure that the LTE and WiFi will both achieve their respective throughput constraints, the DRX active ratio µ must be carefully chosen. If µ is larger, the LTE DL throughput will become larger, but WiFi UL throughput will become smaller. hence,

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Figure 4.12: Proposed algorithm procedure

the WiFi UL throughput constraint decide the upper bound of µ, and the LTE DL throughput constraint decide the lower bound of µ.

Example 1 WiFi has a constrains of minimum transmission rate of 0.5 Mbps with the average transmission rate of 2 Mbps⇒ 2 Mbps×(1 − µ) ≥0.5 Mbps, µup=0.75 is the upper bound.

Example 2 LTE’s minimum transmission rate = 0.2 Mbps, the average rate = 1 Mbps ⇒ 1 Mbps×µ ≥0.2 Mbps, µlow=0.2 is the lower bound

After these constraints are satisfied, we choose the best DRX active ratio to maximize the throughput with DRX. We can see another example in Fig. 4.13, to comply with the LTE throughput constraint, the DRX parameter can only be chosen from 80/128, 100/160 and 100/128. To comply with the WiFi throughput constraint, the DRX param-eter can only be chosen from 80/128 and 100/160. After we meet throughput constraint, we want to find a optimum parameter to maximize LTE DL throughput such that

arg max

µlow≤µ≤µ^up total throughput (with DRX)⇒ µOptimal (4.1) Thus, UE can report TDM solution indication which is included DRX parameter that UE choose to eNB.

Figure 4.13: Select appropriate parameters

Step 4: Set an active factor β Since the measurement period is finite, the measure-ment result of the throughput may be lower than the statiscal expectation of throughput.

It will result in triggering IDC solution too early and degrading the overall performance.

Here, we use an active factor β to avoid switching frequently.

Step 5: Decide whether to trigger the IDC solution or not when DRX scheme is not active

(a)To trigger DRX: The IDC user will average the LTE DL throughput only in the DL subframe which didn’t not be interfered by WiFi.

(b)Do not to trigger DRX: The IDC user will average the LTE DL throughput throughout all the DL subframe no matter the interference from WiFi will happen.

To compute the expectation of the throughput for both with DRX case (a) and no DRX case (b) while the window size is given, we need to know which LTE subframe is interfered by WiFi. Classifying the LTE subframes into two groups, one suffers from WiFi interference, and the other isn’t interfered by WiFi (see Fig. 4.14). By finding

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the average throughput for the group which aren’t interfered by WiFi, we can know the throughput in on-duration timer after we activate DRX mode. Moreover, we can get expectative throughput, if we activate DRX after considering DRX active ratio. So the throughput after DRX activate is (a)·µ. The average throughput for no DRX case (b) is to average all subframe’s throughput no matter whether it is interfered by WiFi.

During the given measured period, if (a)·µ >(b)·β, β > 1, then we should trigger IDCI solution. β is an active factor to avoid switching frequently from step 4.

Figure 4.14: Classify the LTE subframes to two groups for without and with WiFi interference

After trigger for IDC : If UE operates at TDM solution DRX mode.

Step1: Measure WiFi UL ratio during power saving mode WiFi will be denial until DRX power saving mode is starting.

Step 2: Set a deactivate ratio α, 0 < α≤ 1

Because WiFi UL ratio may change with time, average WiFi UL ratio during limited measured period may be smaller than average WiFi UL ratio during overall simulation time, and it causes deactivating DRX scheme too soon. To avoid deactivate DRX scheme too soon and result in interfere from WiFi seriously, we set a deactivate ratio α.

Step 3: Deactivate DRX

We define the throughput for two situations as follow

(c) The IDC user will average the LTE DL throughput only in the DL subframe in On-duration.

(d) LTE DL throughput constraint

The LTE DL throughput after turning off DRX mode is approach to be (c)×(1 − WiFi UL ratio) because the interference from WiFi. If we want to turn off the DRX mode, we must ensure that LTE DL throughput will still meet LTE DL throughput constrain, we set (c)×(1 − WiFi UL ratio

α ) >(d). The former is a expectative throughput after UE deactivate DRX. α is a robust value from step 2.

⇒WiFi UL ratio≤ (1 −^(d)_(c))× α

If WiFi UL ratio smaller than the threshold then it is time to deactivate DRX.

Figure 4.15: WiFi uplink time and LTE DL throughput (no DRX/Only DRX/Proposed)