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Uplink User Capacity in a CDMA Macrocell with a Hotspot Microcell: Effects of Transmit Power Constraints and Finite DispersionPowerPoint Presentation

Uplink User Capacity in a CDMA Macrocell with a Hotspot Microcell: Effects of Transmit Power Constraints and Finite Dispersion

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Uplink User Capacity in a CDMA Macrocell with a Hotspot Microcell: Effects of Transmit Power Constraints and Finite Dispersion

Shalinee Kishore (Lehigh University)

Larry J. Greenstein (WINLAB-Rutgers University)

H. Vincent Poor (Princeton University)

Stuart C. Schwartz (Princeton University)

IEEE Globecom 2003

Two-Tier Cellular CDMA System Microcell: Effects of Transmit Power Constraints and Finite Dispersion

Macrocell with embedded microcell

- Macrocell and microcell use CDMA over same set of
- frequencies cross-tier interference.
- Users select their base stations according to (slowly-
- changing) local mean path gains.
- Ideal power control by each base is assumed.

- Previous Work: Microcell: Effects of Transmit Power Constraints and Finite Dispersion Uplink user capacity quanitifed assuming
- 1) No constraint on transmit power
- 2) Infinitely dispersive channels*
- (S. Kishore, et al., IEEE Trans. On Wireless Communications, March 2003.)
- Goal: Determine uplink user capacity for this system for
- 1) Finite power constraint
- 2) Finitely dispersive channels†
- *Infinitely dispersive channel: infinitude of strong
- multipaths received signal has constant output power
- after RAKE processing.
- †Finitely dispersive channel: finite multipaths output
- power has variable fading.

Effect of Transmit Power Constraint Microcell: Effects of Transmit Power Constraints and Finite Dispersion

Problem Statement Microcell: Effects of Transmit Power Constraints and Finite Dispersion

Given:

- N total users, NM macrocell and Nm microcell.
- Distribution of user locations.
- Random codes of length W/R, where W is system
- bandwidth and R is user data rate.
- Minimum SINR requirement, G.
- Transmit power constraint, Pmax.
- dmax, max. distance over which users are distributed.

Problem Statement (Cont’d) Microcell: Effects of Transmit Power Constraints and Finite Dispersion

- Path gain between a user and a base is modeled as
- Users choose base station for which its path gain is higher.
- Determine:
- Uplink user capacity such that P[Outage] does not exceed
- some specified value, as a function of Pmax and dmax.

Outage Microcell: Effects of Transmit Power Constraints and Finite Dispersion

Previously: for no transmit power constraint, SINR

requirement can be met if and only if

(K - NM)(K - Nm) > IMIm

where K = W/RG + 1 (single-cell pole capacity),

IM and Im are normalized cross-tier interferences

(random variables).

We computed the probability of not meeting this

condition, given either

1) NM and NmPinf(NM,Nm)

2) N = NM + NmPinf(N)

Outage (Cont’d) Microcell: Effects of Transmit Power Constraints and Finite Dispersion

- System unable to support N users if infeasible and/or if
- transmit power (P) of any one user exceeds Pmax.
- Pr[Outage|N] = Pinf(N) + (1 - Pinf(N))·Pr[P > Pmax|N],
- We determined how to exactly compute and reliably
- approximate Pr[P > Pmax|N].
- Result: Pr[Outage|N] can be solved as a function of
- dimensionless parameter F:

Uplink User Capacity versus Max Power Constraint Microcell: Effects of Transmit Power Constraints and Finite Dispersion

N, Total Number of Users, 5% Outage

F*

Effect of Finitely Dispersive Channels Microcell: Effects of Transmit Power Constraints and Finite Dispersion

Motivation Microcell: Effects of Transmit Power Constraints and Finite Dispersion

- Thus far: considered infinitely-dispersive uplink channel.
- Actual channels have finite number of paths, each with
- variable fading user output signal has variable fading.
- Can model fading with modified path gain: Tij’ =rTij,
- wherer is a unit-mean random variable.
- We examine performance for four channel types:
- Rural Area (RA)
- Typical Urban (TU)
- Hilly Terrain (HT)
- Uniform multipath

Uniform Multipath Channel Microcell: Effects of Transmit Power Constraints and Finite Dispersion

Channel Delay Profile

power

Height of each line is mean-

square gain of a Rayleigh

fading path.

delay

Lp

Number of Paths

- Diversity Factor (DF) measures the amount of multipath
- diversity in channel. Computable for any delay profile.
- Uniform channel has DF = Lp.
- Non-uniform channels with Lp paths have DF < Lp.
- For example, DFRA= 1.6, DFHT= 3.3, and DFTU = 4.0.

- Finite Dispersion: Problem Statement Microcell: Effects of Transmit Power Constraints and Finite Dispersion
- Given:
- Single-macrocell/single-microcell system
- Propagation model with variable fading
- Pmax = Max transmit power level
- dmax = Max distance over which users are distributed
- hW = Noise power
- Determine:
- Uplink user capacity so that Pr[Outage] does not exceed
- some given value (e.g., 5%).
- for the three standard environments, i.e., RA, TU, and HT, as
- functions of F.
- for any environment when F > F*.

Variable Power Fading: Key Results Microcell: Effects of Transmit Power Constraints and Finite Dispersion

- Uplink capacity for RA, HT, and TU terrains: constant over
- F > 0.1 and decreases sharply in F when F < 0.1.
- Capacity reduction relative to infinitely dispersive channel: as much as 15% for the RA environment.
- When F > F*, user capacity in uniform multipath channel
- can be approximated as:

, for Lp > 1.

- Showed uplink capacity is the same for channels with same DF.

Replace Lp in

with DF

DF

Napprox

Non-Uniform

Delay Profile

Uplink User Capacity under Finite Dispersion Microcell: Effects of Transmit Power Constraints and Finite Dispersion

N, Total Number of Users, 5% Outage

Lp, Number of Paths

Conclusion Microcell: Effects of Transmit Power Constraints and Finite Dispersion

- Studied impact of transmit power constraints and finite
- dispersion on uplink user capacity of two-tier cellular
- CDMA system.
- Developed exact analytical methods and reliable
- approximation schemes.
- Quantified effect of maximum power constraints on
- coverage area and capacity.
- Used uniform multipath channel to approximate uplink
- user capacity for finitely-dispersive channels.
- Excellent agreements between analytical approximations
- and simulation results.

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