air interface trainer guide

System Training

GPRS Air Interface

Trainer Guide

6-64463v 3-0

© Nokia Oyj 1 (13)

GPRS Air Interface

The information in this document is subject to change without notice and describes only the product defined in the introduction of this documentation. This document is intended for the use of Nokia Networks' customers only for the purposes of the agreement under which the document is submitted, and no part of it may be reproduced or transmitted in any form or means without the prior written permission of Nokia Networks. The document has been prepared to be used by professional and properly trained personnel, and the customer assumes full responsibility when using it. Nokia Networks welcomes customer comments as part of the process of continuous development and improvement of the documentation.

The information or statements given in this document concerning the suitability, capacity, or performance of the mentioned hardware or software products cannot be considered binding but shall be defined in the agreement made between Nokia Networks and the customer. However, Nokia Networks has made all reasonable efforts to ensure that the instructions contained in the document are adequate and free of material errors and omissions. Nokia Networks will, if necessary, explain issues which may not be covered by the document.

Nokia Networks' liability for any errors in the document is limited to the documentary correction of errors. Nokia Networks WILL NOT BE RESPONSIBLE IN ANY EVENT FOR ERRORS IN THIS DOCUMENT OR FOR ANY DAMAGES, INCIDENTAL OR CONSEQUENTIAL (INCLUDING MONETARY LOSSES), that might arise from the use of this document or the information in it.

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Copyright © Nokia Oyj 2003. All rights reserved.

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Contents

Contents

1 Course preparation..................................................................4

2 GPRS Air Interface.....................................................................5

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2 Course preparation

Sessions General introduction

Materials Training slides, or

PowerPoint-presentation file

Flipchart

Training document

Equipment Whiteboard

Overhead projector (OHP), or

Video projector connected to PC

Empty transparencies

Markers

Preparation The Training Document binders:

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3 GPRS Air Interface

Module GPRS Radio Interface

Subject

Objectives After this training session, the participant should be able to:

Explain the functions of the air interface in the Physical, MAC, and RLC layers

Differentiate between physical and logical GPRS channels

List and describe the GPRS air interface logical channels and their functions

Explain the GPRS TDMA frame, multiframe, and superframe structure

List and compare four different coding schemes and the puncturing concept

Describe multiple timeslot usage

Describe briefly the process of channel allocation in the uplink and downlink

without reference to notes.

Programme Introduction

Air interface layering

GPRS channels

Framing

Channel coding

Radio resource management

Data transfer

Modulation

Materials PowerPoint slides

Training Document: Module: Introduction to TCP/IP

Equipment OH projector or video projector with PC

Flipchart and/or whiteboard

Preparation None

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Trainer Participant Props(equipment)

Overview

Aim

To provide participants information about technical solutions in GPRS air interface and landline transmission..

Time

Depends very much on the interest of your audience, max 4 hours

(average 2 hours)

Experience

Ask each participant about his/her experience in this topic.

Gain

Ask each participant what s/he hopes to gain by this module.

Objectives

Show objectives slide.

Process

The trainer generates flipchart illustrations and uses slides to proceed through the material.

The participants have the training document where the slides are embedded.

The participants have the exercises.

Most of the information presented in class can also be found in the training document.

The trainer will be asking questions throughout the course.

The participants are also encouraged to pose questions.

Contents

Module objectives

Introduction

Layering

outline

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GPRS Channels

Framing

Coding schemes and multiple timeslots

Radio Resource Management

Summary Q&A

Reassurance

In this session the participants will get the general idea of the GPRS Air Interface.

Body

2. IntroductionIntroduction

? Ask participants about the important aspects of the GPRS air-interface.

The air-interface is a limited and most expensive resource that has to be shared with GSM.

Have to manage it carefully

Uplink vs. Downlink

Bottleneck in GPRS performance

Transmission Problems: Noise, Fading, Interference, Multipath.

Asymmetric and independent uplink and downlink channels.

Slide "What is the air interface?"

(Slide 4)

communication concept is presented in slide 5

? What are the important functions associated with the air-interface?

Ask the participant to briefly explain these functions in their own words.

Modulation and Demodulation

Framing

Channel Coding

Error Control

Congestion Control

Medium Access Control

Synchronisation

Multiplexing

Multi-access

Timing Advance

Power Control

Handover

Ciphering

Write participants responses on white board and then display Slide 3

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3. Air Interface Layering

Slide 5 shows the important layers of the MS - GPRS Network.

Initiate an open -ended discussion on the need of having these layers and their functions.

The important layers across the Um interface are RLC, MAC, Physical Link and RF layer. Each layer communicates with the peer entity across the interface.

Slide 5

Slide 6 shows the operation of the layers from the Network layer to the RF layer. This slide should explain the concept of encapsulation, independence of layers and segmentation.

Slide 6

Slides 7-12 explain the functions of the layers identified.

Slides 7-12

4. Additional GPRS channels in GSMoptional: slide 13 to 15 are used for a short repetition of GSM/GPRS radio interface basics

Channels

? Ask the participant what is meant by the following concepts

Spectrum vs. carrier frequency

Physical vs. logical channels.

Traffic vs. control channels (CCH)

Dedicated vs. broadcast channels

Data vs. signalling channels

Uplink vs. downlink channels

Revision of GSM channels

? Ask the participant to name the GSM logical channels and their purpose.

TCH

CCH

FCCH

SCH

BCCH

CCCH

PCH

RACH

AGCH

Write the participants responses on the white board or flip chart. (see slide 16

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SDCH

Revision of GSM channels to physical channel mapping

26 multiframe

51 multiframe

your participants explain the mapping – then GPRS is easy, because the same concept can be found.

slide 17, 18

Radio Block

Radio blocks already exist in GSM (see. SACCH frames). The same concept is in use in GPRS later on.

slide 19

GPRS Logical Channels

Explain the logical channels through an example: The diplomat turns the MS on in Singapore, what does the GPRS MS do? What channels are needed? You can also present the channels and procedures as flows with advanced groups. In that case, remember to check out the flows in the GPRS Air Interface specifications.

PBCCH Packet Broadcast Control Channel is a downlink only channel for broadcasting system information.

PCCCH Packet Common Control Channels (PCCCH) consists of logical channels used for common control signalling.

PRACH Packet Random Access Channel is an uplink only channel, which the MSs use for uplink traffic channel reservation. Also the normal GSM RACH can be used for this in case there is no PCCCH allocated in the cell.

PPCH Packet Paging Channel is a downlink only paging channel used to page the MS before a downlink packet is transferred. The normal GSM PCH can be used for GPRS in case there is no PCCCH allocated in the cell.

PAGCH Packet Access Grant Channel is a downlink only channel used for resource assignment. The normal GSM AGCH (Access Grant Channel) can be used in case there is no PCCCH allocated in the cell.

PNCH Packet Notification Channel (only in GPRS Phase2) is a downlink only channel used for the PTM-M notifications before PTM-M packet transfer.

PDTCH Packet Data Traffic

slide 20 to 25,

esp. slide 25

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Channel is reserved for the actual GPRS data transfer.

PACCH Packet Associated Control Channel is a signalling channel dedicated for a certain MS.

PTCCH Packet Timing advance Control Channel is used in uplink direction for the transmission of random access bursts to estimate the timing advance for a mobile. In the downlink direction one PTCCH is used to transmit timing advance information to several MSs.

Revision of GSM channels to physical channel mapping

51 multiframes and

52 multiframe.

Focus on 52 multiframes, which are new.

discuss the analogy between GSM and GPRS with your participants.

slide 27, 28, 29, esp. slide 28.

Explain the physical channel framing. Here you might also be required to draw parallels between the multiframe structure in GSM and GPRS. You could show and explain the GSM control channel multiframe slide to address any such query.

The participant has to understand the framing hierarchy

Bursts in TS

Frames (8 TS)

Radio Blocks (4 Bursts in 4 consecutive frames in the same TS position)

Multiframes (12 RB + 2 Idle + 2 PTTCCH)

Superframe

Hyperframe

The GPRS physical channel is called Packet Data Channel (PDCH).

Different packet logical channels can be transported in the same physical channel.

Mapping of different GPRS logical channels to a PDCH using a multiframe structure.

The PDCH multiframe has 52 radio frames.

One multiframe consists of twelve Radio Blocks (of four radio frames each), two idle frames and two frames for PTCCH.

MSs can also share a single timeslot in uplink direction.

Assigning radio blocks of one

Slides 23-33.

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PDCH to different MSs is done by the MAC layer.

Allocation may be static or dynamic.

5. GPRS Multislot CapabilitiesMultislot Operation ? What is multislot operation and why is it used?

1-8 air interface timeslots can given to a user for higher rate connections.

The BSS selects coding scheme, number of allocated timeslots and number of radio blocks in a timeslot

Balance: number of users and data rates.

Show slide 31 on Multiple timeslot allocation.

6. Coding SchemesName the different CS and explain what is actually done.

Slide 30 shows the processing involved from MAC data block into interleaved bursts in a radio block.

Slide 33 shows the format of the radio block at various stages.

Slide 34 shows the data rate computations for CS-1 to CS-4 (Details are given in Training Document)

Four possible air interface coding schemes: CS1, CS2, CS3 and CS4 are possible in GPRS.

CS-1 only error detection is possible whereas error correction is possible with other.

Puncturing is used in CS-2 and CS-3.

In Nokia GPRS release 1, the coding schemes CS1 and CS2 are supported.

What do you think - can we reduce the error coding without having any effect?

What is required if we reduce error coding (higher C/I ratio=> new cells)?

Ask why CS1 & CS2 would only be supported in Nokia GPRS release 1.

Air interface throughput rate for each coding scheme in different carrier to interference ratios.

The simulations were made for two cases: with one timeslot and three timeslots allocated for GPRS.

Remember that this throughput could be shared by several users.

The current GSM networks have a C/I of around 15.

With that level of C/I CS-2 would give a little above 10 kbit/s, CS-1 and CS-3 around 8 kbit/s and

slide 38

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CS-4 1 kbit/s per timeslot.

In other words, with current cell plans, CS-1 and CS-2 are the viable options.

7. Radio Resource Management

Slide 39 describes how radio blocks are allocated to MS

Slide 40 shows the use of USF flag.

Slide 41 explains the TFI field.

Slide 42 shows the dynamic allocation of timeslots.

Dedicated, default and additional timeslots on the radio interface give a lot of implementation flexibility without compromising with existing CS traffic. CS and PS territories can be defined, and their borders can be shifted dynamically.

Slide 39-41

8. Data TransferData Transfer

Again start with the story of the MS being switched on, performing an RA/LA update and moving into the Ready state (MM context) and ready for packet connection options (PDP context). Now pose the question "How are radio blocks transferred over the air interface, that is, how does the network ensure that the packets from the network are 'picked-up' by the correct MS. And similarly on the uplink, how does the network manage contention arbitration of the same radio resources being sought by multiple MSs?

Explain the concept of resource allocation and reallocation, emphasising the dynamic nature of allocation. Do not digress into details of the RLC/MAC layer, otherwise it will open up a Pandora's box! For the more curious participants, distribute a handout.

For the messages, you could use animations on the slides to put across the concepts in a better and user-friendlier manner.

Uplink packet transfer is initiated by a Packet Channel Request that could go either on the RACH or PRACH.

The network considers the resources demanded with the packet channel request and allocates resources to the MS by the Packet Immediate Assignment message, which goes on the AGCH (PAGCH), and also carries PC and TA information. This completes the Phase 1 access.

Phase 2 access (optional) is initiated by the MS if it is seeking more resources for uplink data transfer.

The packet resource request message from the MS carries the description of the requested resources for uplink transfer.

The network responds with a packet resource assignment message indicating the resources reserved for uplink transfer as well as PC and TA information.

Both are sent on the PACCH.

Show 43-45

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Start by asking the impact of implementing GPRS on existing networks in terms of traffic handling capabilities. Then move on to the flexible options that Nokia offers to seamlessly integrate GPRS into existing cells, in a phased manner. Explain the concept of 'Territories'.

Sum up the chapter with a review of key points and ASK QUESTIONS!

Mobile terminated packet transfer is also quite similar, except that the Packet Resource Assignment message includes the list of PDCH(s) that will be used for downlink transfer as well as the PDCH carrying the PACCH.

9. ModulationThis part is optional. If your participants are interested in the EDGE-GPRS solution, you can use this chapter to outline the 8PSK modulation concept.

Important note: Within EGPRS, different Modulation and Coding Schemes (MCS) than in GSM-GPRS are applied!

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air interface trainer guide

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