wiki:Manual/Main/CdmaEngine

You are here: Manual / Main / CDMA

TracNav


CDMA / OFDMA Simulation Engine

Click on the below link to get directly to the section of this page:

Introduction

Whereas traditional simulation of non-CDMA (or non-OFDMA) systems is carried out in SEAMCAT by taking two pairs of transmitters-receivers and estimating signals received between them separately (i.e. without any form of feed-back influence), the simulation of cellular systems requires a much more complex process of power controlling in a fully loaded system, including impact from two tiers of neighbouring cells and, for victim cellular systems, the attempt by the system to level-out the interference impact.

Therefore SEAMCAT supplements a single considered CDMA / OFDMA cell with its Base Station (BS) two tiers of virtual cells to form a 19 cell (57 cell for tri-sector deployment) cluster, which is then populated with a certain number of mobile stations (MS) and a power control algorithm is then applied for balancing overall system, see Figure below:

For CDMA system, before the actual simulations start, the CDMA engine may run the special algorithm for finding the non-interfered (optimal) capacity of the defined CDMA system. Alternatively, you may define the load of modelled CDMA system. The OFDMA modelling does not have such algorithm.

Then, in case of CDMA system being the interferer, the CDMA engine balances it only once, then notes the transmit powers and positions of relevant transmitters (BS or MS, depending on scenario) and sends them back to EGE as Interfering Transmitters for calculation of iRSS. If the CDMA system is a victim, at first the power balancing is done without the external interferer considered, the achieved in a snapshot number of connected CDMA users (i.e. MSs) noted, and then the external interferer is introduced and CDMA system is re-balanced again. Afterwards the number of served users, compared with that before interference was introduced, allows estimating impact of interference in terms of excess outage brought to the system. Therefore, for CDMA victim, the impact of interference is established through the combined work of EGE and CDMAE modules and does not require subsequent run of ICE.

If both victim and interferer systems are CDMA, then the combination of the above is applied.

Normally the considered cellular system (CDMA or OFDMA) is modelled as endless network using the so called wrap-around technique. Alternatively, you may specify that the modelled cellular cell is laying at the edge of the network, in this case the cellular system will be modelled as if extending to one side only. The latter case may be suitable for simulation of geographically separated victim and interfering systems, like in cross-border scenarios.

The simulation of OFDMA systems is similar to that of the CDMA systems, except that after the overall two-tiers cellular system structure (incl. wrap-around) is built and populated with mobiles, the CDMA power tuning process is replaced in OFDMA case with an iterative process of assigning a variable number of traffic sub-carriers and calculating the overall carried traffic per base station.

The current OFDMA module has been designed for a Long Term Evolution (LTE) network from 3GPP (TR36.942(3)). Therefore E-UTRA RF coexistence studies can be performed with Monte-Carlo simulation methodology. The detailed simulation flow for DL and UL can be found in Annex 14 of the SEAMCAT handbook (January 2010).

CDMA overview

The CDMA module on-line manual is split in different entities:

Note: It should be noted that the term "CDMA" is used in this documentation and in SEAMCAT environment in general to refer to any radio technology that employs the Code Division Multiple Access modulation scheme. The specific CDMA standard (e.g. CDMA2000-1X, or W-CDMA/UMTS) can be selected by incorporating the appropriate link level curves into the simulation scenario. Furthermore, at present, only the interference impact of/on "voice" can be studied using SEAMCAT.

OFDMA overview

The OFDMA module on-line manual is split in different entities:

CDMA OFDMA commonalities

Cellular topology in SEAMCAT

It should be noted that SEAMCAT has been based on a 3GPP2 hexagonal grid and the following figures illustrates the differences. CDMA and OFDMA module are sharing the same module.

3GPP 3GPP2 - SEAMCAT

In some ECC Report treating of 3GPP simulation(1)(2), the following notations, as show below, are used:

Cell Radius = R1
Cell Range = 2R1
BS to BS distance = 3R1


Illustration of the Cell Radius, Cell Range and BS to BS distance according to 3GPP terminology.

The following notations, as shown below, are used within SEAMCAT (3GPP2 based):
Cell Radius = R
Cell Range = h = sqrt(R2-R2/4)
BS to BS distance = 2h

Illustration of the Cell Radius, Cell Range and BS to BS distance according to 3GPP2 terminology and implemented in SEAMCAT.



What is important is that the site-to-site or base station-to-base station distance be the same between the 3GPP and the 3GPP2 approach, i.e. where 3R1= 2h. From there it is possible to extract the cell radius in SEAMCAT.

Example of the distances relationship between 3GPP and SEAMCAT Example of SEAMCAT GUI results to check the BS to BS distance

Pathloss and Effective Pathloss

In SEAMCAT, there is a distinction between the raw pathloss and the effective pathloss. The effective pathloss conisders the minumum coupling loss (MCL) as defined in 3GPP. The MCL is the parameter describing the minimum loss in signal between BS and UE or UE and UE in the worst case and is defined as the minimum distance loss including antenna gains measured between antenna connectors. Note that the effective path loss includes shadowing.

The effective pathloss is defined such as:

where:

  • GTx : antenna gain at the transmitter (Tx) in dBi.
  • GRx : antenna gain at the receiver (Rx) in dBi.

Note: The MCL is an input parameter to SEAMCAT. Typical values of MCL can be found in 3GPP documents(3). By defaults this value is 70 dB (i.e. typical value for Macro cell Urban Area BS <-> UE for frequency of 2000 MHz, e.g., there is a difference between 900 MHz and 2500 MHz with respect to MCL.) when defining the victim or interferer OFDMA system, but the value is set to 0 dB, when the MCL is used in the It->Vr path.

Reference Cell

Part of configuring a cellular network is selecting the reference cell. The reference cell is used by SEAMCAT to measure results and all none reference cells are used to provide a proper interference background to the reference cell. Note: when “Measure interference from entire cluster” is checked, all the transmitters are used when simulating the interference (i.e. all the 19/57 BS or all the Ues in all the cells). When it is not checked, it is only the reference cell which is the interferer. This feature only applies when a CDMA network is the source of interference. For OFDMA, the algorithm consider all the transmitters as interferer by default.

Wall attenuation in CDMA-OFDMA module

In some cases when simulating CDMA or OFDMA system, wall attenuation is to be considered to simulate UEs being inside or outside a building. Each links are generated independently from each other therefore it is not possible to introduce an extra wall loss directly into the propagation model (built-in or plugin), otherwise a UE being inside a building and connected to a BS site would have 3 different random draw of the wall attenuation (in 3-sector case). Instead it is recommended adding an extra attenuation to the antenna gain. It will allow each user to have an omni-directional antenna (usually 0 dB) and wall attenuation by setting a User Defined (stair) distribution. The example below is for a case where 50% of UE have 0 dB and 50%, 10 dB.

References

(1) ECC Report 82: Compatibility study for UMTS operating within the GSM 900 and GSM 1800 frequency bands
(2) ECC Report 96: Compatibility between UMTS 900/1800 and systems operating in adjacent bands
(3) 3GPP, Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA);Radio Frequency (RF) system scenarios

Attachments