September 2007
IEEE P802.19-07/0020r0-mg
IEEE P802.19
Wireless Coexistence
Project
IEEE P802.19 Coexistence TAG
Title
Coexistence Metrics for the 3650 MHz Band
Date
Submitted
[September 5, 2007]
Source
[Stephen
J.
Shellhammer] Voice:
[Qualcomm,
Inc.] Fax:
[5775 Morehouse Drive]
E-mail:
[San Diego, CA 92121]
Re:
[]
Abstract
[A set of coexistence metrics are proposed for evaluation of coexistence of
802.11y and 802.16h in the 3650 MHz frequency band]
Purpose
[]
Notice
This document has been prepared to assist the IEEE P802.19. 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 acknowledges and accepts that this contribution becomes the
property of IEEE and may be made publicly available by P802.19.
Submission
Page 1
[(858) 658-1874]
[(858) 651-3004]
[shellhammer@ieee.org]
Steve Shellhammer, Qualcomm, Inc.
September 2007
IEEE P802.19-07/0020r0-mg
1 Introduction
The coexistence metrics for the 802.11y and 802.16 both operating in the 3.65-3.7GHz band
should be appropriate for the deployment scenarios which will be used in the band. We see three
different deployment scenarios and usage of a channel by 802.16h and 802.11y technologies:
Scenario 1: many almost co-located cells, for which the cell size is such that there are only
few hidden stations on the channel.
Scenario 2: large cells, for which most of the stations will be hidden due to the high power of
the energy detection levels.
Scenario 3: mix of large and smaller cells.
We consider that part of the operator coordination process will be an agreement on the frequency
channel allocation for the different deployment scenarios. This implies that for those systems
sharing a channel the protocols and the coexistence metrics should be tailored to each
deployment scenario.
The scope of the coexistence simulation will be to assess the coexistence properties of the
802.11y and 802.16h protocols and to identify the specific protocols or protocol adaptations
suitable for each scenario.
The choice of metrics is intended to uncover potential problems that could arise when these two
networks share the same spectrum. Members of 802.11, 802.16 and 802.19 are developing a
document summarizing the simulation parameters used to evaluate the coexistence of these two
networks [1]. This document is intended as a companion document that will describe the various
coexistence metrics to be used in the simulations to evaluate the coexistence of these two
networks.
2 Coexistence Metrics for Scenario 1
In order to give an accurate description of the coexistence metrics one must say a few words
about how the simulation is to be designed. After the design of the simulation is explained the
definitions of the coexistence metrics will be given.
The simulation consists of two networks: an 802.11y network and an 802.16h network. Each
network contains an access point (also called a base station) and a set of client stations. These
Submission
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Steve Shellhammer, Qualcomm, Inc.
September 2007
IEEE P802.19-07/0020r0-mg
networks are in close proximity to one another. One of spatial simulation parameters is the
distance between the 802.11y access point and the 802.16h access point. That distances is fixed
for a number of experiments. For each experiment client stations will be placed randomly within
the coverage area of the respective networks. For each of these experiments the simulation will
be run for a fixed period of time. Source data traffic is being simulated at the access points to be
sent to the various clients and source data traffic is being simulated at the client stations to be
sent to the access point. The data traffic statistics are specified in [1].
For each experiment there are several performance parameters that can be specified. These
parameters are used to specify the coexistence metrics.
For each experiment there are N links between the access point (either 802.11y or 802.16h) and
the client stations. The downlink traffic flows from the access point to the clients and the uplink
data flows from the clients to the access point. For each experiment we define the following four
parameters for each of the two networks,




The uplink throughput for each of the N links in the network
The downlink throughput for each of the N links in the network
The uplink latency (from top-of-the-MAC to top-of-the-MAC) for each of the N links in
the network
The downlink latency (from top-of-the-MAC to top-of-the-MAC) for each of the N links
in the network
These four parameters are random variables that depend on the placement of the client station.
So for each experiment we have a probability density function for each of these four random
variables. We then run M experiments, in each experiment randomly placing the clients. So
these random variables have a distribution over the number of experiments and multiple clients
in each experiment. We summarize these random variables as follows,
TPUL
Uplink throughput
TPDL
Downlink throughput
LUL
Uplink latency
LDL
Downlink latency
Given these four random variables we can define the coexistence metrics. We are interested in
averages of these random variables since that gives an indication of average coexistence effects.
However, we are not only interested in averages since averaging can hide some interference
effects on individual clients. For example, we want to be able to measure the effects of hidden
node effects that can occur in CSMA networks [2]. A hidden node could result in low throughput
or long latency for a small subset of clients. In order to measure these types of effects we need to
consider the tail probabilities of these random variables. In other words we need to measure the
Submission
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Steve Shellhammer, Qualcomm, Inc.
September 2007
IEEE P802.19-07/0020r0-mg
throughput (or latency) value at which the majority of clients attain that throughput value. In
order to measure both average values and these tail probabilities we will use the cumulative
distribution function of these four random variables. Let FX(x) be the cumulative distribution
function of the random variable X. We will use for coexistence metrics the 50% and 95% value
of these for distributions. These are represented as F-1(0.5) and F-1(0.95) for the four random
variables, where F-1() is the inverse of the cumulative distribution function. The 50% value is
called the median. The 95% value will simply be referred to as the 95% value. In summary the
coexistence metrics are,
Median Uplink throughput
Median Downlink throughput
Median Uplink latency
Median Downlink latency
95% Uplink throughput
95% Downlink throughput
95% Uplink latency
95% Downlink latency
3 Coexistence Metrics for Scenario 2
In the case of the large cells scenario, we consider that the system will use a channel either
selected or agreed by the operators. The procedures described below shall be followed. These
procedures are applied for the each instance of the simulation. There are two steps for each
instance of the simulation, being two layers in the first step:
Step 1:
In the first layer, is calculated the cell size for each system (BS and its stations) based on the
system gain at the minimum considered data rate (QPSK ¼) from which are subtracted M dB for
the intra-system interference. In our case M shall be (t.b.d – 6-7 dB?) It is chosen "a priori" Base
Station spatial density and based on this is taken for each instance of the simulation a random
distribution for BS and its Subscriber Stations. In this layer the two operators do not interact each
with the other. It is established which is the actual C/(Ii+N) – the level of the desired carrier
signal versus the intra-system interference, for each receiver i.
In the second layer, it is assessed the Ci/(Ie+N), being considered the interference caused by the
2nd operator.
Step 2:
Submission
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Steve Shellhammer, Qualcomm, Inc.
September 2007
IEEE P802.19-07/0020r0-mg
In this step it is assessed the degradation of the C/(Ii+N) for each receiver, due to the interference
caused by the second operator. It can be derived the statistics of the degradation or it can be set a
threshold (1dB or 2dB degradation as threshold).
It is no requirement to use data rates or delays as coexistence metrics, because these are related to
the C/(I+N) statistics.
A simplified (initial) version of the simulation may assume the fix and uniform distribution of
the BS and of stations of an operator and the random distribution of the cells for another
operator.
The coexistence metric is represented by the statistics of the C/(Ii+N) degradation.
4 Coexistence Metrics for Scenario 3
Scenario 3 will have as target to preserve the cell size in the large deployment scenario and to
insure a high spectrum efficiency and QoS. The coexistence metrics will address the parameters
and the procedures defined for the previous scenarios.
5 References
[1]
Paul Piggin, Parameters for simulation of Wireless Coexistence in the US 3.65GHz
band, IEEE 802.19-07/11r7, September 2007
[2]
Steve Shellhammer, Clear Channel Assessment Energy Detection (CCA-ED) in
802.11y, IEEE 802.19-07/10r1, May 2007
Submission
Page 5
Steve Shellhammer, Qualcomm, Inc.