GSM, 3G-WCDMA, LTE and the Road to 5G

From the 1990s to today, three generations of mobile radio networks have been installed in every country in the world. The book's final section deals with further development towards the next generation of mobile networks (5G).

Acknowledgements

EDGE Enhanced Data Rate for GSM Evolution E-DPCCH E-DCH Dedicated Physical Control Channel E-HICH E-DCH Hybrid ARQ Indicator Channel EIR Equipment Identity Register. HS-DPCCH Fast dedicated physical control channel HS-DSCH Fast shared downlink channel.

Introduction

Types of Mobile Network by Multiple-Access Scheme

Cellular System

Historical Background
Cellular Concept
Carrier-to-Interference Ratio
Formation of Clusters
Sectorization
Frequency Allocation
Trunking Eﬀect
Erlang Formulas
Erlang B Formula
Worked Examples

Problem 1
Problem 2
Problem 3

Interference power (from other cells) (3.1) The intensity of the interference is essentially a function of co-channel interference, depending on the frequency reuse distance D. If in the example here the dependence of the beam path loss is slower had been (i.e. the propagation exponent was less than 4), the required cluster size would have been greater than 7, thus the path loss. features have a direct impact on system capacity.

Figure 3.1 Model of a cellular network with frequency reuse. Shadowed hexagons represent cells with the same set of allocated frequencies.

Radio Propagation

Propagation Mechanisms

Free-Space Propagation
Propagation Models for Path Loss (Global Mean) Prediction

Averaging over the fast fading structure gives the local average of the propagation path loss or received signal strength. However, the detailed structure causes random variations in the local average of the signal received by the mobile unit (called shadow fading, slow fading or normal fading).

Figure 4.1 Path loss examples with diﬀerent clutter loss factors.

Mobile Radio Channel

Channel Characterization

Narrowband Flat Channel
Wideband Frequency Selective Channel
Doppler Shift

The most important parameter of the power delay profile is the delay range or RMS delay range. The result of the composition of multipath components with different Doppler shifts is the Doppler power spectrum of the received signal.

Worked Examples

Problem 1
Problem 2

However, it has no direct impact on most other broadband systems (such as single-carrier Time-Division Multiple-Access (TDMA) or Code Division Multiple-Access (CDMA) systems). 2) It is a measure of the temporal variability of the channel. Assume that the Doppler power spectrum has a bandwidth of Δf ∼𝜈max= fcvmax∕c and introduce a 'stationary' interval of the channel; that is, the time interval in which the channel can be considered constant.

Fading

Shadowing/Slow Fading
Fast Fading/Rayleigh Fading

In Figure 5.10, the cell range would be about 8 km if the shadow effect were neglected, then only 50% of the locations at the edge of the cell would be adequately covered. During fade-downs, the instantaneous signal level drops 10-15 dB below the average level (the local average, i.e. the value after the average over the slow fade).

Figure 5.9 Probability density function of signal variations normalized at the global mean.

Diversity to Mitigate Multipath Fading

Space and Polarization Diversity

In the opposite case of waves arriving at the base station antenna from an individual mobile station, arriving waves are concentrated in a narrow angular sector, thus illustrating a plane wave. The mechanism of polarization diversity is based on the observed fact that polarization of a radiated wave becomes random due to multiple scattering in the multipath channel.

Worked Examples

Problem 1
Problem 2
Problem 3

What are the minimum values of Δfh given that the delay spread of the communication channel is Δ𝜏=5μs?. Assuming a typical moving neighborhood with no line of sight, we have the case for isotropic scattering, 𝜗s=180∘. Spatial correlation interval isl= 𝜆∕2, temporal correlation interval istc= l∕v=𝜆∕2v=5 ms. 2) the maximum Doppler shift is Δf = v∕𝜆.

Receiver Noise Factor (Noise Figure)

Any physically realizable system introduces additional noise on top of the thermal noise floor. The noise figure is defined as the ratio between the SNR at the input and the SNR at the output of the receiver.

Radio Network Planning

Generic Link Budget

Receiver Sensitivity Level
Design Level

Rayleigh Fading Margin
Lognormal Fading Margin
Body Loss
Car Penetration Loss
Design Level
Building Penetration Loss
Outdoor-to-Indoor Design Level

Power Link Budget
Power Balance

Path balance means that the downlink coverage is equal to the uplink coverage. When the uplink is weaker, the mobile station can receive the signal of the base station on the downlink, but the base station cannot "hear" the mobile phone.

Table 6.2 Typical values of building penetration loss.

Worked Examples

Problem 1
Problem 2
Problem 3

Apparently, in the case of a weaker uplink path we should take MAPL=MAPLUL as allowable path loss. Assuming that the coverage range beyond the break point sets distanced0, we can consider path loss at the distanced>d0, that is.

Global System Mobile, GSM, 2G

General Concept for GSM System Development

GSM System Architecture

Location Area Identity (LAI)
The SIM Concept
User Addressing in the GSM Network
International Mobile Station Equipment Identity (IMEI)
International Mobile Subscriber Identity (IMSI)
Diﬀerent Roles of MSISDN and IMSI
Mobile Station Routing Number
Calls to Mobile Terminals
Temporary Mobile Subscriber Identity (TMSI)
Call Security
Operation and Maintenance Security

The LAI determines the exact location of the MS where the mobile can next be paged. By means of the country code and the NDC, the fixed network (eg PSTN or ISDN) establishes a connection to the carrier gateway (GMSC).

Radio Speciﬁcations

Spectrum Eﬃciency
Access Technology
MAHO and Measurements Performed by Mobile
Time Slot and Burst

Normal Burst
Frequency Correction Burst (FB)
Synchronization Burst
Access Burst
Dummy Burst

GSM Adaptation to a Wideband Propagation Channel

Training Sequence and Equalization
The Channel Equalization
Diversity Against Fast Fading
Frequency Hopping

The training sequence is used to "sound" the radio channel and produce an estimate of its impulse response at the receiver. The received training sequence is used to estimate the impulse response of the radio channel in the channel estimator.

Background for the Choice of Radio Parameters

Guard Period, Timing Advance

To prevent data bursts from different terminals from overlapping at the input to the base station receivers, a guard period (GP) with a time of 8.25 bits ~ 31 μs has been introduced. The delay is adjusted so that a transmitted burst from the terminal reaches the base station receiver at the correct position relative to the time slot structure.

Figure 7.17 TDMA frame length constraints.

Communication Channels in GSM

Traﬃc Channels (TCHs)
Control Channels

Common Control Channels
Dedicated Control Channels

Full-rate data channels: payload data with data rates of 9.6, 4.8 or 2.4 kbps are encoded with Forwards Error Correction (FEC) codes and transmitted at an effective data rate of 22.8 kbps. Different logical channels are used at different stages of the call setup procedure, see Figure 7.20.

Mapping the Logical Channels onto Physical Channels

Frame Format
Transmission of User Information: Fast Associated Control Channel

Data Rates

Signalling Multiframe, 51-Frame Multiframe
Synchronization

Frequency Synchronization
Time Synchronization

Signalling Procedures over the Air Interface .1 Synchronization to the Base Station

Registering With the Base Station

The MS listens to the SCH and FCCH of the neighbor cells during the IDLE frame in a traffic channel cycle of a 26-frame multiframe. Based on the receipt of the RACH, the BS can estimate the round-trip time between the BS and the MS and use this information to advance the timing (described in the next section).

Signalling During a Call

Measuring the Signal Levels from Adjacent Cells
Handover

Intra-Cell and Inter-Cell Handover
Intra- and Inter-BSC Handover
Intra- and Inter-MSC Handover
Intra- and Inter-PLMN Handover
Handover Triggering

Power Control

The decision for a handover is made by the BSC based on the uplink and downlink measurements taken by the MS and BS respectively. During the call, the BSC continuously monitors these measurements taken by the MS and BS.

Signal Processing Chain

Speech and Channel Coding
Reordering and Interleaving of the TCH

Class 1a includes bits for which transmission errors result in a strong interruption of the output signal from the speech decoder. Assigned to class 1b are bits for which transmission errors result in a fairly large degradation of speech quality.

Estimating Required Signalling Capacity in the Cell

SDCCH Conﬁguration
Worked Example .1 Problem 1

An example of cell capacity is given in Table 7.4 where the Erlang capacity of the cell with 2% congestion probability varies with the configuration of signaling and traffic channels in cells with different numbers of receivers. Give the BTS configuration in terms of the number of TRXs and control channels defined for a cell.

Table 7.4 Erlang capacity of the cell versus number of TRX.

By calculating the link budget, we obtain an allowable path loss at uplink and downlink estimates of 140.1 dB and 154.1 dB, respectively. SDCCH Erlang/cell required – 0.6 Erl, resulting in three time slots required for SDCCH per cell with 2% GoS.

EGPRS: GPRS/EDGE

GPRS Support Nodes
GPRS Interfaces
GPRS Procedures in Packet Call Setups
GPRS Mobility Management

Mobility Management States .1 IDLE State
PDP Context Activation
Location Management

Layered Overview of the Radio Interface

SNDP
Layer Services
Radio Link Layer
GPRS Logical Channels
Mapping to Physical GPRS Channels
Channel Sharing
EGPRS Channel Coding and Modulation

GPRS/GSM Territory in a Base-Station Transceiver

PS Capacity in the Base Station/Cell

Summary

Finally, the SGSN updates its PDP context table and confirms the activation of the new PDP context to the MS (ACTIVATE PDP CONTEXT ACCEPT). In IDLE state, no location update is performed; that is, the current location of the MS is unknown.

Third Generation Network (3G), UMTS

The WCDMA Concept

Spreading (Channelization)
Scrambling
Multiservice Capacity
Power Control

Open-Loop Power Control
Outer-Loop Power Control

Handover

Softer Handover
Other Handovers
Compressed Mode

RAKE Reception

The OVSF orthogonality property ensures that different users of the same cell do not interfere with each other. This is only possible if the code sequences of different chip streams are orthogonal to each other. The OVSF codes can be created using code tree, as illustrated in Figure 9.7.

Major Parameters of 3G WCDMA Air Interface

The output symbols from different fingers are multiplied with complex conjugation of the channel estimate and the result of multiplication is added together in the 'combined' symbol. As shown in Figure 9.17, the receiver uses known lead symbols used to sound the channel and provide an immediate estimate of the channel state (value of the weighted phasor) for a particular finger.

Spectrum Allocation for 3G WCDMA

The received symbol is then reversed to undo the phase rotation caused by the channel. Such channel compensated symbols can then simply be added to recover the energy across all delay positions.

Table 9.3 Comparison of GSM and WCDMA in air-interface technology.

9.4 3G Services

Bearer Service and QoS

The layered architecture of a UMTS carrier service is depicted in Figure 9.18; each bearer service at a particular layer offers its individual services through those provided by the layers below. The QoS parameters are given by the core network to the radio network in a radio access bearer configuration.

UMTS Reference Network Architecture and Interfaces

The NodeB (Base Station) Functions in the 3G Network
Role of the RNC in 3G Network The RNC is responsible for the following

The actual fast power control is performed at the NodeB, but the target control values are set at the RNC. The RNC cyclically allocates the transmission capacity to individual MSs, at the same time taking into account the negotiated QoS.

Air-Interface Architecture and Processing

Physical Layer (Layer 1)
Medium Access Control (MAC) on Layer 2
Radio Link Control (RLC) on Layer 2
RRC on Layer 3 in the Control Plane

The user plane consists of transport channels and physical channels allocated for the connection and the data transferred over the connection. The physical layer supports information transfer to the MAC and higher layers via transport channels.

Figure 9.20 Air-interface protocol reference architecture [9].

Channels on the Air Interface

Logical Channels
Transport Channels

Dedicated Transport Channel (DCH)
Common Transport Channels

Physical Channels and Physical Signals
Parameters of the Transport Channel

Transmission of Random Access Channel (RACH), which is used for random access by the UE and for transmission of a small amount of data in the uplink direction. The TFC defines the number of transport blocks transmitted from each of the multiplexed transport channels in a given TTI.

Figure 9.21 shows a simpliﬁed example for grouping services/applications according to QoS and mapping the logical, transport and physical channels.

Physical-Layer Procedures

Processing of Transport Blocks
Spreading and Modulation
Modulation Scheme in UTRAN FDD
Composition of the Physical Channels .1 Dedicated Physical Channel

Common Downlink Physical Channels

After modulation, this would result in signals with a high crest factor (i.e. the peak-to-average power ratio), which would lead to distortion of the amplified signal. Uplink The composition of the dedicated physical channel in the uplink direction is shown in Figure 9.28.

Figure 9.22 Multiplexing the transport channels.

RRC States

Idle Mode
RRC Connected Mode
RRC Connection Procedures
RRC State Transition Cases

The MS can enter the cell _FACH state from idle mode by setting up the RRC connection. The RRC Connection Setup message may contain a specific physical channel assignment for the UE (transition to Cell_DCH state), or it may instruct the UE to use shared channels (transition to Cell_FACH state).

Figure 9.34 RRC states and state transitions including GSM and E-UTRA [16].

RRM Functions

Admission Control Principle
Load/Congestion Control
Code Management
Packet Scheduling

Depending on the amount of application data to be transmitted, service delay, signal load and network resource utilization, the UE may be allowed to use either Cell_DCH or Cell_FACH mode. Upon receiving the paging message, the UE moves to the Cell_FACH state and initiates signaling on the RACH, as illustrated in Figure 9.37.

Figure 9.38 Estimation of load increase caused by the admission of additional traﬃc.

Initial Access to the Network

The base station provides the air interface load measurements and the mobile provides uplink traffic volume measurements to the packet scheduler. The user-specific scheduling controls the utilization of RRC modes, transport channels and their bit rates according to the traffic volume.

Summary

This is because all users on the uplink interfere with each other, and the goal of power control is to reduce intra-cell interference by equalizing the received power per bit of all mobile stations at all times. During softer/softer handover, two tight power control loops are active to solve the near-far problem in both cells.

High-Speed Packet Data Access (HSPA)

HSDPA, High-Speed Downlink Packet Data Access

A specific number of codes available for HS-DSCH transmission is configurable between 1 and 15 and can be dynamically assigned to a single user, as shown in Figure 10.1 and Figure 10.2. In support of the assigned set of channelization codes, a certain transmitter power is allocated for HS-DSCH transmission.

HSPA RRM Functions

Channel-Dependent Scheduling for HS-DSCH
Rate Control, Dynamic Resource Allocation, Adaptive Modulation and Coding
Hybrid-ARQ with Soft Combining, HARQ
Retransmission Mechanism in the NodeB
Impact to Protocol Architecture
HARQ Schemes

The NodeB keeps the number of packets in the buffer even after they are sent to the UE. The transfer of RRM functions, such as fast scheduling and packet retransmission, to the NodeB leads to the changes in protocol architecture.