|
|
|
Research Activities > PhD |
|
 |
 |
 |
The objective of the testbed is to emulate the UTRAN over an Ethernet local network taking care of different properties such as the handling of UMTS transport channels, the emulation of time-correlated errors at Layer 3, the emulation of two of the three RLC modes and finally, the derivation of the BER of a mobile user. |
 |
Each of the data flows is mapped to one of the three available UMTS transport channels:
- The Dedicated CHannel (DCH),
- The Dedicated Shared CHannel (DSCH), or
- The Forward Access CHannel (FACH).
|
|
| The emulation of the Radio Link Control (RLC) and Med-ium Access Control (MAC) layers is achieved using the Linux Traffic Controller and an adapted version of the NetEm module including a modified Gilbert-Elliot model. We define a burst as a number of subsequent erroneous TTIs whereas a gap is a number of subsequent error-free TTIs: |
|
   |
|
|
| The RLC layer is able to transmit RLC PDUs in three different modes: Acknowledged Mode (AM), Unacknowledged Mode (UM) and Transparent Mode (TM). We decided to focus on two of them, namely the TM likely to transmit the delay-sensitive RT traffic. On the other hand, we use the AM for NRT traffic to lower the packet error rate. Those two modes have been adapted to an Ethernet link and included in the enhanced version of the NetEm module. |
|
  |
|
| Periodically, the received power of each User Equipment (UE) is computed, so as to derive the quality of the on-going transmission. This power is a direct function of the NodeB emitted power and is also influenced by a number of factors. On the DCH, the target Eb/N0 setpoint is permanently adjusted and aims at a constant quality, usually defined as a certain target BER, depending on the traffic class. Following specifications, we have fixed the target BER. Conversely, the associated DSCH benefits from the same transmit power. However, as a different spreading factor can be allocated to the DSCH, the resulting BER can vary. Finally, the FACH is transmitted at constant power, such that its BER degrades when the mobile user moves away from the NodeB. |
|
 |
|
PhD
