Title / Proposed changes to the 802.20Channel Models Document (802.20 PD-08)
Date Submitted / 2007-1-16 (Jan16, 2007)
Source(s): / Anna Tee
Samsung Telecommunications America
K. Sivanesan
Samsung Electronics, Suwon, S-Korea / Voice: 1 (972) 761-7437
Email:
Email:
Re: / 802.20 Channel models document
Abstract / This document proposes updates to the 802.20 channel models document, specifically the models for system-level simulations.
Purpose / This document proposes updates to the 802.20 channel models document, to resolve some of the issues that have been discussed at the 802.20 Plenary meeting on Tuesday, Nov 14, 2006.
Notice / This document has been prepared to assist the IEEE 802.20 Working Group. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release / The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.20.
Patent Policy / The contributor is familiar with IEEE patent policy, as outlined in Section 6.3 of the IEEE-SA Standards Board Operations Manual and in Understanding Patent Issues During IEEE Standards Development
- Introduction
During the Working Group (WG) meeting in November 2006, issues on the IEEE 802.20 channel models document [1] has been discussed [2].
In addition, Chapter 2 on SISO channel models requires clarifications on the assumptions made for the path loss models. Path loss models as specified in Table 2.2-1 are applicable to 1900 MHz carrier frequency only. As the base path loss models (COST-231) are functions of carrier frequency, use of the path loss models as specified in the Table for a different carrier frequency could produce significantly different results.
This contribution outlines a few suggestions to resolve the ambiguities and improve the channel models document.
- Proposed changes to the channel models document
- Title
As mentioned in Section 1.1, the purpose of this document is to specify channel models for simulations of MBWA air interface schemes at link level, as well as at system level. For consistency, the title may be modified as follows:
‘IEEE 802.20 Channel Models Document for IEEE 802.20 MBWA System Simulations’
- Chapter 2 SISO Channel models
This Chapter consists of two sections, each with a Table of parameters. The following modifications with descriptive text may help to clarify the use of these Tables. Some important assumptions for the path loss models in section 2.2 may lead to incorrect evaluation results. For example, when the carrier frequency is different from 1900 MHz, the path loss models will be different from those shown in the Table.
‘SISO systems shall use the ITU Channel models in simulations.’
2.1 Link Level Simulation
The parameters for the ITU channel models for link-level simulations are summarized in Table 2.1-1. The speeds shown for each power delay profile (PDP) are example values. Other mobile speeds may also be used with these PDP.
…
[Table 2.1-1]
2.2 System Level Simulation
The channel scenarios and their corresponding parameters for the path loss and shadowing models as listed in Table 2.2-1 shall be used in the system-level simulations. Definitions for various channel scenarios are described in Section 3.4.
Channel Scenario / Suburban Macro(Phase I) / Urban Macro / Urban Micro
Lognormal shadowing standard deviation / 10dB / 10dB / NLOS: 10dB
LOS: 4dB
Pathloss model (dB),
d is in meters / 31.5 + 35log10(d) / 34.5 + 35log10(d) / NLOS:34.53+38log10(d)
LOS:30.18 + 26*log10(d)
Table 2.2-1 SISO Channel Environment Parameters
The path loss models as specified in the Table assume a carrier frequency of 1900 MHz. For other carrier frequencies, the path loss models should be modified based on the original versions of COST-231 models as described below:[A1]
- The macrocell pathloss is based on the modified COST231 Hata urban propagation model:
where is the BS antenna height in meters, the MS antenna height in meters, is the carrier frequency in MHz, d is the distance between the BS and MS in meters, and C is a constant factor (C = 0dB for suburban macro and C = 3dB for urban macro). Setting these parameters to = 32m, = 1.5m, and =1900MHz, the path-losses for suburban and urban macro environments become, respectively, and . The distance d is required to be at least 35m.
- The microcell NLOS pathloss is based on the COST 231 Walfish-Ikegami NLOS model with the following parameters: BS antenna height 12.5m, building height 12m, building to building distance 50m, street width 25m, MS antenna height 1.5m, orientation 30deg for all paths, and selection of metropolitan center. With these parameters, the equation simplifies to:
PL(dB) = -55.9 + 38*log10(d) + (24.5 + 1.5*fc/925)*log10(fc).
The resulting pathloss at 1900 MHz is: PL(dB) = 34.53 + 38*log10(d), where d is in meters. The distance d is at least 20m. A bulk log normal shadowing applying to all sub-paths has a standard deviation of 10dB.
- The microcell LOS pathloss is based on the COST 231 Walfish-Ikegami street canyon model with the same parameters as in the NLOS case. The pathloss is
PL(dB) = -35.4 + 26*log10(d) + 20*log10(fc)
The resulting pathloss at 1900 MHz is PL(dB) = 30.18 + 26*log10(d), where d is in meters. The distance d is at least 20m. A bulk log normal shadowing applying to all sub-paths has a standard deviation of 4dB.
A PDP based on the ITU channel models as shown in Table 2.1-1 may be assigned to each user in the simulated cellular sectors, according to a desirable percentage mix as described in the evaluation criteria document [3].
The simulation results based on these channel models are comparable to those of MIMO systems. Please see Section 3.5 for example of how the correlation matrix approach to MIMO channel models collapses to the ITU-R model for SISO systems.
For calculations using a center frequency as a variable, for example path loss, 1900 MHz is assumed.
See Section 3.4 for Definitions
- Section 3.6MIMO Correlation Channel Matrices
Non-SISO systems mayshalluse [A2]a correlation matrix approach in simulations. The correlation matrices are only antenna system dependent. The correlation matrices may be generated by using the SCM approach (SECTION 6) or computed analytically based on the PAS distribution and array geometry (SECTION 7). The matrices used shall be submitted as part of the simulation report. There are two matrices that need to be considered, the transmit correlation matrix (TCM) and the receive correlation matrix (RCM).
1.6.23.6.2Generation of a MIMO Channel Using Correlation Matrix Approach
Some of the parameters that can be used in the correlation channel model are shown in Table 3.52.2-1. [A3]In [A4]order to generate a MIMO channel, we first need to have a pair of transmit and receive and correlation matrices. These are generated for each mobile station (MS) and base station (BS) based on the number of antennas, antenna spacing, number of clusters, power azimuth spectrum (PAS), azimuth spread (AS), and angle of arrival (AoA). In addition to the correlation matrices, we also need to specify an underlying ITU SISO model from Table 3.52.2-1 and choose the mobile speed
…
3. Color the tap gain matrix by the receive and transmit correlation matrices as follows
17
If the SCM method in Section 6 is used to generate the transmit and receivecorrelation matrices, with N Tx antennas M Rx antennas:
(i) Receive correlation matrix (MXM) can be written as
.
(ii) Transmit correlation Matrix (NXN) can be written as
.
where is the channel coefficients vector of i-th transmit antenna to the M-Rx antennas (i-th column of HSCM ) and is the channel coefficients vector of j-th Rx antenna to the N-Tx antennas (j-th row of HSCM ). HSCM is given by the expression in Section 6.2. The average is taken over all the possible transmit or receive antennas, N multipaths, and simulated channel realizations t. The recommended minimum number of channel realizations is 10000.
- Other editorialchanges to Tables 2.1-1, 2.2-1, 3.7-1
-Delete the ‘Editor notes’ from the Tables, after checking for consistency with evaluation criteria document;
-Remove ‘Phase 1’ [A5]from the Table, unless the phased approach in the evaluation criteria document is restored;
-Remove extra row and column from Table 2.2-1;
- 3GPP/3GPP2 Spatial Channel Models (SCM)
Even though the WG has previously anticipated a need to compare SISO with MIMO technology proposals, there has not been any actual use of [A6]this comparison in the WG since the presentations on the proposals in November 2005[5].
Therefore, it is evidential that the need to have the comparison between SISO and MIMO may not exist. On the other hand, for future proposals to be able to achieve comparable performance levels as the earlier proposals, it is likely that these new proposals will also support MIMO technology. Thus, there will be a need to compare between different MIMO proposals. [A7]
A detail review of the current channel models document reveals that Chapters 4 through 6 are adopted from the original 3GPP/3GPP2 spatial channel models (SCM) document. As described in Section 4.1 (quoted below), these chapters define the methodology for generating both the spatial and temporal MIMO channel model coefficients used for the system-level simulations of 802.20.
4.1Introduction
The spatial channel model for MBWA system-level simulations is described in this chapter. As in the link level simulations, the description is in the context of a downlink system where BS transmits to a MS; however the methodology described here can be applied to the uplink as well. The goal of this chapter is to define the methodology and parameters for generating the spatial and temporal MIMO channel model coefficients for MBWA system simulations[A8].
Based on the discussions from the November 2006 meeting [7], some of the proposals that had been previously adopted by 802.20 as the standard draft may not have been evaluated using the spatial channel models as described in Chapters 4 through 6 of the channel models document. [A9]
In any case, it is suggested that all proposals, including past and future submissions, should be evaluated using the same spatial channel models as described in Chapters 4 through 6 for a fair comparison. As discussed in the November ’06 meeting [2], the SCM are channel models that include both the temporal and spatial aspects of channels variations in a mobile cellular environment. The SCM has been widely used by various standards organizations in the mobile cellular Industry[A10][8], [9].
- SCM-Extended (SCME) channel models for link-level simulations
[A11]The original SCM has been specified for channel bandwidths up to 5 MHz. Recent work has been done in other standards organizations to extend the SCM to higher bandwidths, which are known as the SCM extended models (SCME). These correlation matrix based models have been recommended for link-level MIMO simulations. A description of the SCME models and the correlation matrices can be found in Annex A of [9].
As some of the 802.20 proposals are targeting bandwidths higher than 5 MHz, the SCME model may be considered as an appropriate model for evaluation of bandwidths above 5 MHz.
- Other channel environments
As indicated in Section 4.2.2 of the Systems Requirements document [11], it is stated that: “The system shall work in dense urban, urban, suburban, rural, outdoor-indoor, pedestrian, and vehicular environments and the relevant channel models shall be applicable.”
Current version of the channel models document has only specified the evaluation of 3 channel environments: suburban macro, urban macro and urban micro.
The evaluation of urban and suburban scenarios only has led to the inadequate evaluation of high mobility user scenarios, which is one of the issues in the evaluation criteria document as discussed in November ’06 meeting [A12][12].
A rural scenario which consists of a significant percentage of high mobility users should be specified for the system-level evaluation of mobility up to 250 km/h [13], as required for the standard [11]. [A13]
Additional channel environments may need to be included for consistency with the systems requirements document.
References
[1]‘IEEE 802.20 Channel Models (V1.0)’, IEEE 802.20 PD-08, Sept, 2005.
[2]‘Comments on Channel Models document’, C802.20-06/34, Nov. 14, 2006.
[3]‘Draft 802.20 Permanent document-Channel models for IEEE 802.20 MBWA System simulations – Rev 07’, Nov. 18, 2004.
[4]‘IEEE 802.20 Evaluation Criteria document (V1.0)’, IEEE 802.20-PD09, Sept., 2005.
[5]‘Presentation on channel models document’, C802.20-06/33,Nov 14, 2006
[6]‘3GPP, TR25.996, “Spatial Channel Model for Multiple Input Multiple Output (MIMO) [‘Spatial Channel Model Text Description’, SCM-135, 3GPP/3GPP2 Spatial Channel Model Ad-Hoc]
[7]‘Revised draft minutes, 802.20 Plenary meeting, Session #21, Dallas, TX, USA, Nov. 12-17, 2006’, 802.20-06/07r2.
[8]‘Overview of the Spatial Channel Model developed in 3GPP-3GPP2’, C802.20-04/79, Nov 15, 2004.
[9]‘3GPP Physical Layer aspects for EUTRA, Release 7’, TR 25.814 v7.1.0, Annex A, Sept. 2006
[10]‘CDMA 2000 Evaluation Methodology-Revision 0’, 3GPP2 C.R1002-0 Version 1.0, December 10, 2004.
[11]‘IEEE 802.20 Systems Requirements Document (V1.0)’, IEEE 802.20 PD-06r1, July 2004.
[12]‘Presentation on evaluation criteria document’, C802.20-06/35, Nov 15, 2006
[13]‘Proposed changes to the 802.20 traffic modeling and evaluation criteria document’, Jan 15, 2007.
[A1]Suggest replace “The entries in the table above are generated based on the COST-231 models as described below”
[A2]Restore “shall” to enable comparison.
[A3]Is this the right Table number?
[A4]Table 5.5-1
[A5]Change to “Report I”
[A6]Not true.
[A7]Should not restrict the technology submission to MIMO technology.
[A8]Add clarification to the 3rd step.
[A9]“may not have been”?
[A10]Correlation approach has similar feature.
[A11]Remove
[A12]two staged approach with separate link study works well.
[A13]rural area is usually not capacity limited, system capacity is not very interesting.