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Two-Stage Dynamic Uplink Channel and Slot Assignment for GPRS
Author: Ying-Dar Lin, Yu-Ching Hsu, Mei-Yan ChiangReporter: Chen-Nien Tsai
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Outline
GPRS Background Introduction Two-Stage Dynamic Channel and
Slot Assignment Results Summary
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GPRS Background
GPRS Introduction GPRS Network Architecture GPRS Air Interface GPRS Logical Channels Mapping Logical Channels to
Physical Channels Packet Data Transfer Operations
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GPRS Introduction
GPRS: Stands for General (or generic) Packet
Radio Services developed by European
Telecommunication Standard Institute (ETSI)
is one of the standards of Global System for Mobile communications (GSM) Phase 2+
is designed as a packet switching system
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GPRS Network Architecture
It fits in with the existing GSM PLMN Two new network elements
Serving GPRS Support Node (SGSN) Gateway GPRS Support Node (GGSN)
Many new interfaces Gb, Gi, Gn, etc.
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GPRS Network Architecture
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GPRS Air Interface (1/3) GPRS uses the existing GSM resources. GPRS uses a two-dimensional access schem
e (FDMA and TDMA). Total 25 MHz bandwidth 125 carrier frequencies of 200 kHz bandwidth
GPRS users will share the same TDMA frame with GSM voice users.
GPRS air interface will dynamically allocate resources (timeslots).
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GPRS Air Interface (2/3) TDMA Frame
8 timeslots Period = 4.615 ms
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GPRS Air Interface (3/3)52 Multiframes
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GPRS Logical Channels
PDCH is the generic name for the physical channel allocated to carry packet logical channels
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Mapping Logical Channels to Physical Channels (1/3) Logical channels are carried on
physical channels. Multiple logical channels can be
mapped onto the same physical channels.
Three possible combinations: PBCCH+PCCCH+PDTCH+PACCH+PTCCH PCCCH+PDTCH+PACCH+PTCCH PDTCH+PACCH+PTCCH
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Mapping Logical Channels to Physical Channels (2/3)
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Mapping Logical Channels to Physical Channels (3/3)
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Packet Data Transfer Operations
Before data can transfer GPRS Attachment PDP (Packet Data Protocol) context
activation. After these two steps, the mobile
can access the network, request resources, and send data.
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Uplink Packet Data Transfer Request resources
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Uplink Packet Data Transfer Fixed radio block allocation
According to bit map
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Uplink Packet Data Transfer
Dynamic radio block allocation USF (Uplink State Flag) is
attributed to each MS.
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Outline
GPRS Background Introduction Two-Stage Dynamic Channel and
Slot Assignment Results Summary
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Introduction
Two-stage assignment Stage-1: BS assigns several PDCHs to an
MS. Stage-2: BS selects one of the multiplexe
d MSs in a PDCH to use the radio resource. Objective of this paper
Load balance in stage-1 Good prediction in stage-2
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Outline
GPRS Background Introduction Two-Stage Dynamic Channel and
Slot Assignment Results Summary
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Two-Stage Dynamic Channel and Slot Assignment
Stage 1 Multiple PDCHs with the corresponding U
SFs are assigned to an MS. Stage 2
To utilize the radio resource, the BS has to predict who has data to send and the assign the following time slot to that MS.
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Stage-1 Channel Assignment After receiving the Packet Channel Request,
BS must decide the number of as well as which specific PDCHs to be assigned to the MS.
Deciding which PDCHs to assign is more critical. (load balance)
Two load measurement methods Number of Assigned Flow Effective transmission over last cycle
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Number of Assigned Flow (NoAF) The number of multiplexed MSs withi
n a PDCH is chosen as the load measurement metric.
This scheme can be considered a frequency-wise and PDCH-wise balance.
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Effective Transmission over Last Cycle (EToLC) The load metric employed by EToLC is
defined as the number of transmissions occurred during the previous PRR (Pure Round-Robin) cycle.
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Stage-2 Slot Assignment The BS has to predict who has data to
send. If the selected MS has no data
impending, the slot is wasted. Three schemes are considered:
Pure Round-Robin Round-Robin with Linearly-Accumulated
Adjustment Optimal
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Pure Round-Robin (PRR)
Each multiplexed MS in a PDCH is round-robined to use the uplink channel.
All MSs are assumed having impending data to send.
A PRR cycle equals the number of MSs multiplexed in this PDCH.
The highest mis-selection rate.
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Round-Robin with Linearly-Accumulated Adjustment (RRLAA)
Basis principle to reduce the transmission chance for th
e MSs that failed to utilize the last assigned slot, and increase the chance for those who had.
For RRLAA, a Penalty cycle and a Reward cycle are defined and appear alternately.
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Penalty Cycle (1/2) A Penalty cycle is derived from PRR cycle by
skipping MSs who waste their last assigned timeslots in Penalty cycles.
An MS will be skipped in n successive penalty cycles when it wastes n successive assigned timeslots in Penalty cycles.
When the MS begins to send packets, the penalty accumulation is reset.
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Penalty Cycle (2/2)M: number of multiplexed MS in a PDCH
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Reward Cycle (1/2) An MS is authorized to transmit during the
following Reward cycle if it transmits data in the previous Penalty cycle.
An MS will be rewarded n timeslots in a Reward cycle when it successively employs the assigned timeslots in n penalty cycles.
An MS will be selected to send data at most once in a Penalty cycle but possibly multiple times in a Reward cycle.
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Reward Cycle (2/2)Infinite loop?
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Optimal (OPT) Assume that whether an MS has data to
send or not is known in advance. For compare performance.
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Outline
GPRS Background Introduction Two-Stage Dynamic Channel and
Slot Assignment Results Summary
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Results
Comparison between Load Balancing Schemes for Stage-1 Channel Assignment
Comparison between Selection Schemes for Stage-2 Slot Assignment
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Comparison for Stage-1 Channel Assignment (1/3)
FNoP-NoAF is designed to be compared with other three models and is considered as the most load-balanced case.
RND: Random FNoP: Fixed Number of PDCH (?)
NoAF: Number of Assigned Flow
EToLC: Effective Transmission over Last Cycle
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Comparison for Stage-1 Channel Assignment (2/3) Standard deviation of PDCH utilization
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Comparison for Stage-1 Channel Assignment (3/3) System throughput
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Comparison for Stage-2 Slot Assignment (1/3) Mis-selection rate
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Comparison for Stage-2 Slot Assignment (2/3) System throughput
throughput ≈ offered load * ( 1 – mis-selection rate)
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Comparison for Stage-2 Slot Assignment (3/3) Average Packet Queuing Delay
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Outline
GPRS Background Introduction Two-Stage Dynamic Channel and
Slot Assignment Results Summary
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Summary (1/2)
Two load-balancing schemes for stage-1 channel assignment. Number of Assigned Flow (NoAF) Effective Transmission over Last Cycle (E
ToLC) EToLC outperforms NoAF.
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Summary (2/2)
One selection scheme for stage-2 slot assignment. Round Robin with Linearly-Accumulated
Adjustment (RRLAA). Reward and penalty cycles.
RRLAA has the lower mis-selection rate, better system throughput, and lower packet queuing delay.