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Here we have to mention that some differences
between real and estimated load factor value may
occur, as a consequence of inaccuracies in the
measurement of the other-to-own-cell interference
and path loss.
Algorithm execution follows the flow shown on
Figure 1. Assuming n already granted transmissions
and initially selected TF for n+1 request, the Kraft’s
inequality is evaluated, the expected load factor is
compared with a threshold φ and expected
transmission power should be below the maximum
transmitted power. If all tree conditions are satisfied,
transmission is granted for this request during one
TTI, otherwise, the transport format is reduced by
one (i.e. transmission bit rate is reduced). If this is
not possible, the request should wait for the next
frame.
5 SIMULATION SCENARIO
The system model includes 7 omnidirectional base
stations. Distance between two neighboring base
stations is 1 km. Maximum transmitted power by the
base station is 43 dBm. Mobile users are uniformly
distributed in the scenario moving with speed of 50
km/h. At each position update (every TTI) we
assume that mobile user will change his direction to
left or to right in 45° with probability 0.1 for each
side, and probability 0.8 that he will stay on previous
course. Path loss model used in this simulation is
adopted from (3GPP TS 25 942) and path loss
calculations are made according to (10).
L = 128.1 + 37.6 Log10(R) (10)
R is a distance from BS to ME. Path loss
calculated buy (10) shall in no circumstances be less
than free space path loss – FSPL = 20log(4πR/λ) . If
during calculations L become smaller than FSPL,
then FSPL should be considered instead L as path
loss.
After L (FSPL) is calculated, log-normally
distributed shadowing (LogF) with standard
deviation of 10 dB should be added, so that the
resulting path loss is the following:
Pathloss = L + LogF (11)
Number of voice, video and www users is taken
to be on of the parameters which will be changing
during simulations.
Traffic generation model proposed in (Perez-
Romero, 2002)(3FPP TR 101 112-UMTS 30.03) is
used, including following parameters for:
- Conversational Service (Voice traffic): On-Off
model with 0.3 activity factor. In the active period
voice users generates 160 bits in 10 ms (16 kbps).
- Interactive Service (WWW traffic): Session
arrival process – Poisson process; Number of packet
call requests per session – geometrically distributed
with mean 5 calls per session; Reading time between
packet calls – geometrically distributed with a mean
33 [s]; Number of packets within a packet call –
geometrically distributed with a mean value 25; Inter
arrival time between packets – geometrically
distributed with a mean 0.0625 [s] (for 64 kbps);
Packet size – Pareto Distribution (with cut-off), max
packet size 66666 bytes with parameters α=1.1,
k=81.5.
- Video Streaming Basic and Enhancement
Service: CBR model; bit rate 32 kbps (each 40 ms
packet with 1280 bits is generated);
In our simulations we have adopted: 40 ms for
TTI (Transport Time interval), 320 bits Transport
Block Size for WWW and Video streaming service
and 160 bits Transport Block Size for conversational
service. DCH used for transmission of voice and
video streaming basic layer will have two transport
formats (TFs): TF0 – no transmission and TF1
transmission of 4 Transport Blocks (TBs) in TTI.
Transport formats for DSCH, used for transport of
WWW and video streaming enhancement layer, are
listed in Table 1.
Table 1: Transport Formats for Downlink Shared Channel
(DSCH)
TB sizes, bits 320 bits (payload) + 16 bits
(MAC/RLC header)
TF0, bits
0×320
TF1, bits
1×320 (8 Kb/s)
TF2, bits
2×320 (16 Kb/s)
TF3, bits
4×320 (32 Kb/s)
TF4, bits
8×320 (64 Kb/s)
TFS
TF5, bits
16×320 (128 Kb/s)
TTI, ms 40
Duration of this simulation corresponds to 3 min
in real time. Life time of voice and video services
packets was set to 1s and for www service to 10s. If
the packet remains in the buffer longer then his life
time it will be discarded.
ICETE 2004 - WIRELESS COMMUNICATION SYSTEMS AND NETWORKS
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