Simulation Scenarios

The simulation environment is set based on 3GPP specification defined in [113]. A sce- nario of 19 hexagonal cells is conducted with the reference cell surrounded by two ties cells. The detailed system parameters and settings are listed in Table 3.1 [42] [116] [14]. The wireless channel is modelled in terms of distance-dependent path loss, shadowing fading and multipath Rayleigh fading with each independent fading path generated by Jakes Model [15]. The traffic flow for the user is modelled as the Poisson process.

• Multi-cell topology: the network topology in the designed LTE-A simulator con- sists of 19 hexagonal cell as shown in Fig. 3.7. The centre cell provides the network service for the UE in the middle; other 18 cells continuously generate the interfer- ence and noise to the UE for simulating the practical network condition.

UE

Figure 3.7: Multi-cell Topology for LTE-A System Simulator

• CC configuration: 4 CCs are adopted at the spectrum band of 2.0 GHz; each CC is assigned with the bandwidth of 10 MHz and has 50 Physical Resource Blocks (PRBs); each PRB has 12 subcarriers; thus each CC has up to 600 subcarriers at one time slot (1 ms).

Given the network topology and CC configuration, the structure of the LTE-A sim- ulator is represented in Fig. 3.8, consisting of traffic generator module, user mobility management module, channel generator module, eNBs and UEs.

• Traffic generator module: the maximum number of user per cell is set to be 80, 20% of which is LTE-A users. The traffic generator module is used to simulate downlink traffic from Internet to UEs; the traffic for the ith UE will be generated according to

Poisson process with the generation rateli, in the unite of the packets per second.

The total traffic eNB received can be described as a Poisson process with arrival ratelt, calculated bylt=Â80i=1li.

Traffic Generator Module

SINR Mapping to Transmission Rate CUM Scheduling Algorithm User Mobility Management Module Channel Generator Module Calculating SINRs and CQIs

eNBs

UEs

Uplink Downlink

Figure 3.8: Component Structure of LTE-A Simulator.

• User mobility management module: user mobility management module is used to generate and manage UE locations; at the start of each simulation, the UEs will be randomly positioned in the centre cell with coordinate [x,y], given a random speed

value, v, and a random mobility angle, q. During the simulation, the users will

move a certain distance in the centre cell at each TTI. User mobility management module will use the following equations to update the UE locations:

x_inew=xold_i +vi⇤ T T I ⇤ cos(qi) (3.14)

ynew_i =yold_i +vi⇤ T T I ⇤ sin(qi) (3.15)

In order to avoid the user cross the cell edge, user mobility management module will check the distance between UEs to the eNB at each TTI and change the mobility direction if the distance is larger than the cell radius. UE locations data generated by the mobility module will be stored in an excel document in advance. During the

Table 3.2: Channel Parameters in Hata Model

f (GHz) hB(m) hM(m) d(Km)

2 150 1 5

simulation, eNBs will read the position data from this file to acquire the locations of UEs, calculate the channel quality and process resource allocation strategy. • Wireless Channel Model: several factors are considered in the simulator to simulate

wireless channel, including shadow fading [117], multi-path Rayleigh fading [118] and distance-related path loss [119].

• Pathloss model: Hata model [120] is widely used in wireless communications to estimate the channel behaviour such as diffraction, reflection and scattering. As the working spectrum is set to be 2 GHz, COST 231-Hata model [121] is used in the simulator to estimate the path loss.

PHata=46.3 + 33.9 ⇤ log( f /1MHz) b(hB/1m) a(hM/1m)+

(44.9 6.55log(hB/1m))log(d/1Km) +CM

(3.16)

The parameters in Eq. (3.16) are listed in Table 3.2, where f is the carrier frequency,

hB and hM are heights of BS and UE respectively, and d is the distance between BS

and UE.

For the small-medium network size, the value of CM in COST 231 Hata model is

set to be 0; and the values of a(hM), b(hM)are calculated by

a(hM) = (1.1log( f /1MHz) 0.7) ⇤ hM/1m 1.56log( f /1MHz) + 0.8 (3.17)

• Shadow fading: shadow fading, due to the presence of the large obstruction, ob- scures the wireless signal between the eNBs and UEs. It is modelled by a log- normal distribution with 0 mean and 8 dB of standard deviation in the simulator [122]. Shadow fading for the ith UE on the jth RB at the time t is denoted as Si, j(t).

• Multi-path Rayleigh Fading: Jake Model [123][124] is adopted in the simulator to

model the multi-path Rayleigh fading, denoted as Mi, j(t). Jake Model has good

characteristic to capture the effect of the user mobility such as Doppler effects. With the path-loss model, shadow fading and multi-path Rayleigh fading, the overall channel gain, Gi, j(t), can be calculated as [120]

Gi, j(t) = 10(Pi, j(t)/10)⇤ 10(Mi, j(t)/10)⇤ 10(Si, j(t)/10) (3.19)

Based on the achieved channel gain, UEs leverage the approach in [120] to calcu- late the Signal Interference plus Noise Rate (SINR) and forward the SINR together with Channel Quality Index (CQI) to eNB [125]; Once eNB receives the SINR and CQI infor- mation, it maps the SINR to transmission rata that UEs can be achieved and conducts the proposed CUM algorithm.