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Radio network planners, particularly, face a number of new challenges when moving from the familiar 2G to the new 3G networks, many of them related to the design and the planning of true multi-service radio networks, and some to particular aspects of the underlying WCDMA radio access method.

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This training course gives detailed descriptions and important features of of the radio network planning and design of UMTS networks based on Frequency Division Duplex (FDD) for WCDMA technology.

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Network planning faces real constraints. Operators with existing networks may have to co-locate future sites for either economic, technical or planning reasons. Greenfield operators are subject to more and more environmental and land use considerations in acquiring and developing new sites.

In general, all 3G systems show a certain relation between capacity and coverage, so the network planning process itself depends not only on propagation but also on cell load. Thus, the results of network planning are sensitive to capacity requirements, which makes the process less straightforward.

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Ideally, sites should be selected based on network analysis with the planned load and traffic/service portfolio.

This requires more analysis with the planning tools and immediate feedback from the operating network.

The 3G revolution forces operators to abandon the ‘coverage first, capacity later’ philosophy.

Furthermore, because of the potential for mutual interference, sites need to be selected in groups.

This fact should be considered in planning and optimisation.

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The technology for accessing a network and transporting the information will become

less important, but greater emphasis will be put on the services and the quality

thereof. Users will no longer even know which access technology they are using –

they will just request a service and the network will decide at the time the optimum

technology (GSM/EDGE, cdma2000, WCDMA, WLAN, DVB, etc.) to provide it.

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The forecast is that the Operations Support System (OSS) and especially the value

adding components of the NMS are the areas to expand the business in IT as well as in

telecommunications. This new trend evolves partly because the vision of the new

service-driven future is becoming clearer. Further, the convergence of different

technical solutions will set requirements also to OSS business.

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A radio channel can be fully characterised by its time-variant impulse response, h(t).In

a mobile radio channel, the impulse response consists of several time-delayed

components This kind of channel is referred to as a multipath channel.

The delayed peaks are due to reflections from surrounding objects, and

time dependence is caused by the movement of the User Equipment (UE) and the other

objects in the environment

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At the transmitter site, the first step is modulation in which the narrowband

signal Sn, which occupies frequency band Wi, is formed. In the modulation process,

bit sequences of length n are mapped to 2^n different narrowband symbols constituting the narrowband signal Sn.

In the second step the signal spreading is carried out, in which the narrowband signal Sn is spread in a large frequency band Wc. At the receiver site the first step is despreading.

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Radio propagation characterization is the bread and butter of communications

engineers. Without knowledge of radio propagation, a wireless system

could never be developed. Radio engineers have to acquire full knowledge

of the channel if they want to be successful in designing a good radio

communication system. Therefore, knowledge of radio propagation characteristics

is a prerequisite for designing radio communication systems.

Multipath fading is due to multipath reflections of a transmitted wave by local scatterers

such as houses, buildings, and man-made structures, or natural objects such as forest

surrounding a mobile unit.

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Shadow fading is used to model variations in path loss due to large obstacles like buildings, terrain conditions, trees.

Shadow fading is also called as log-normal fading since it is modeled using log-normal distribution

In cell dimensioning/link budget shadow fading is taken into account through a certain margin (=shadow fading margin)

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In cellular networks there is always co-channel interference. By using various radio resource reuse techniques the impact of interference can be removed.

Yet, the cost of such resource reuse is usually lower overall capacity in the system.

Co-channel interference is a system issue: By proper system design and network planning we can mitigate the cochannel interference partly.

There will be always trade-off between co-channel interference and system efficiency

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Frequency planning is the conventional approach. In frequency planning each cell is

assigned a subset of the available frequencies.

Frequency allocation can be fixed: Each cell has a fixed number of frequencies

Frequency allocation can be dynamic so that each cell may use all (or almost all)

frequencies according to some rule that take into account the traffic variations in

the network

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Adjacent channel interference should be also taken into

account in network planning.

Adjacent channel interference can be mitigated also through proper frequency planning

Adjacent channel interference is usually taken into account in specifications regarding to HW requirements

Adjacent channel interference needs to be kept in mind also in network planning.

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In CDMA all users in the same cell share the same frequency spectrum simultaneously

In a CDMA-based cellular network this is also true for users in different cells.

In spread spectrum transmission the interference tolerance enables universal frequency reuse.

This underlies all other network-level functions. For example, it enables new

functions such as soft handover, but also causes strict requirements for power control.

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In despreading, the wideband signal Sw is converted back to a narrowband signal Sn, which can then be demodulated using standard digital demodulation schemes. Note that the nature of spreading and despreading operation is the same and could be performed by modulation of user data bits by spreading sequence bits.

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There are a number of techniques to spread the information-bearing signal by use of

code signals. Examples are direct sequence, frequency hopping and time hopping

spread spectrum techniques.

The most common technique used in cellular radio networks is the Direct Sequence Spread Spectrum (DS-SS) technique. This is used, for example, in WCDMA technology and in the IS-95 standard.

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Transmission (Tx) side with DS

Information signal is multiplied with channelization code => spread signal

Receiving (Rx) side with DS

Spread signal is multiplied with channelization code

Multiplied signal (spread signal x code) is then integrated (i.e. summed together)

If the integration results in adequately high (or low) values, the signal is meant for the receiver

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The figure illustrates both the data and the spreading and despreading operations

applied to it. The processing gain is given by the ratio of chip rate to the user data rate

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The basic idea is that the receiver works as a correlation receiver, which means that it

correlates a known (reference) code signal with an incoming signal that is composed of

several different CDMA signals (from different users or channels), of general interference

(from other RF systems), and of noise (of thermal nature).

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The PG comes from spreading and coding. Multiple chips are processed to interpret the value of a single information bit.

Hence the processing gain can be expressed as follows:

PG = 10log( W / Rinfo).

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The processing gain is different for different services over 3G mobile network (voice, web browsing, videophone) due to different bit rates

Thus, the coverage area and capacity might be different for different services depending on the radio network planning issues

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The most significant change in Release. ’99 by 3GPP.

UTRAN is subdivided into individual radio network systems (RNSs), where each RNS is controlled by an RNC

UMTS defines four new open interfaces

Uu: UE to Node B (UTRA, the UMTS W–CDMA air interface)

Iu: RNC to GSM Phase 2+ CN interface (MSC/VLR or SGSN)

Iu-CS for circuit-switched data

Iu-PS for packet-switched data

Iub: RNC to Node B interface

Iur: RNC to RNC interface, not comparable to any interface in GSM

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The most significant change in Release. ’99 by 3GPP.

UTRAN is subdivided into individual radio network systems (RNSs), where each RNS is controlled by an RNC

UMTS defines four new open interfaces

Uu: UE to Node B (UTRA, the UMTS W–CDMA air interface)

Iu: RNC to GSM Phase 2+ CN interface (MSC/VLR or SGSN)

Iu-CS for circuit-switched data

Iu-PS for packet-switched data

Iub: RNC to Node B interface

Iur: RNC to RNC interface, not comparable to any interface in GSM

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The universal mobile telecommunication system (UMTS) is a 3G wireless system that

delivers high-bandwidth data and voice services to mobile users. UMTS evolved from

global systems for mobile communications (GSM). UMTS has an air interface based on

W-CDMA and an Internet protocol core network based on general-packet radio service

(GPRS).

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UMTS is an umbrella term for the third generation radio technologies developed within 3GPP.

The radio access specifications provide for Frequency Division Duplex (FDD) and Time Division Duplex (TDD) variants, and several chip rates are provided for in the TDD option, allowing UTRA technology to operate in a wide range of bands and co-exist with other radio access technologies.

UMTS includes the original W-CDMA scheme using paired or unpaired 5 MHz wide channels in globally agreed bandwidth around 2 GHz, though subsequently, further bandwidth has been allocated by the ITU on a regional basis.

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Bit rates up to 2Mbps

• Variable bit rate to offer BW on demand

• Multiplexing of services with different quality requirements on a single

connection (speech, video, data)

• Quality requirements from 0.1 FER (frame error rate) to 10−6 BER

• Coexistence of 2G and 3G and inter-systems handovers

• Support of asymmetric uplink and downlink traffic (like ADSL: WEB

implies more downlink traffic)

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Radio network controller (RNC)

Owns and controls the radio resources in its domain

Radio resource management (RRM) tasks include e.g. the following

Mapping of QoS Parameters into the air interface

Air interface scheduling

Handover control

Outer loop power control

Call Admission Control

Setting of initial powers and SIR targets

Radio resource reservation

Code allocation

Load Control

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Wideband CDMA was selected for a radio access system for UMTS (1997)

(Actually the superiority of OFDM was not fully understood by then)

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WCDMA was studied in various research programs in the industry and universities

WCDMA was chosen besides ETSI also in other forums like ARIB (Japan) as 3G technology in late 1997/early 1998.

During 1998 parallel work proceeded in ETSI and ARIB (mainly), with commonalities but also differences

Work was also on-going in USA and Korea

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The current 3G and 3.5G mobile communication and the variants thereof will surely

not be the end of the development, even though with HSDPA and HSUPA the 3GPP

radio access will be highly competitive for quite some years.

Next-generation systems denoted as fourth generation (4G) are

around the corner and will ensure competitiveness even in the longer run.

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The main additional requirements compared with the current 3G systems can be seen

in particular in that these new systems will be developed for an optimised, pure packet

switched data access with a much more distributed radio resource and network

management (fully IP-based) and a multi-carrier radio access (allowing more flexible

carrier bandwidths than the current 5 MHz).

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Soft handover is a form of diversity, increasing the signal-to-noise ratio when the transmission power is constant. At network level, soft handover smoothes the movement of a UE from one cell to another. It helps to minimise the transmission power needed in both uplink and downlink.

Because of universal frequency reuse, the connection of a Mobile Station (MS, or

generally UE in WCDMA) to the cellular network can include several radio links.

When the UE is connected to more than one cell, it is said to be in soft handover

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If, in particular, the UE has more than one radio link to multiple cells on the same site, it is in softer handover.

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The Macro Diversity Combining (MDC) gain is the reduction of the required Eb/N0

per link in soft or softer handover when compared with the situation with one radio link

only. Due to the power control, the gain is small when measured as the average required Eb/N0.

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Power control ensures that each user in the network receives and transmits just enough energy to convey information while causing minimal interference to other users. This is crucial for network capacity.

A secondary reason for power control is to minimise battery consumption.

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The stronger the received common pilot signal power, the less initial transmission power is needed. This type of initial power adjustment is arranged by uplink open-loop power control.

The process has to be supported by a priori information which the UE receives on the cell’s Broadcast Channel (BCH).

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Variations in the multi-path channel may mean that a fixed target value of the SIR cannot always guarantee a satisfactory quality target. Therefore the target SIR must be controlled based on the achieved bit error rate or block error rate. If the error rate is too high, the target SIR is increased until the desired error rate is met.

Increasing the target SIR at the receiver end causes the closed-loop power control to increase the transmission power at the transmitter end until the new target SIR is reached. Control of the target SIR is named outer-loop power control.

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. For the WCDMA standard, power control is applied in both the uplink and downlink

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Control of the target SIR is named outer-loop power control.

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Diversity: statistical independence of elements

Beamforming: coherence between elements

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Physical channels

Corresponds to a specific carrier frequency, code, relative phase in I and Q branches

Dedicated and Common Physical Channels

Layered structure of radio frames and time slots

A radio frame = 10 msec = 15 slots/frame

1 frame = 38400 chips, 1 slot = 2560 chips

Slot configuration varies depending on the channel bit rate of the physical channel

# bits/slot different for different physical channels

may vary with time (on a frame by frame basis)

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The high-level functional grouping into Access Stratum (AS) and Non-Access Stratum

(NAS) defined in the 3GPP standard for Radio Interface Protocol Architecture.

The AS is the functional grouping of protocols specific to the access technique.

It includes protocols for supporting transfer of radio-related information, for

coordinating the use of radio resources between UE and access network, and for

supporting the access from the serving network to the resources provided by the

access network. The AS offers services through Service Access Points (SAPs) to

the NAS (CN-related signalling and services) – i.e., provides the access link between

the UE and CN – which consists of one or more independent and simultaneous UE–

CN RAB services, and only one signalling connection between the upper-layer entities

of the UE and CN.

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The radio interface protocols are needed to set up, reconfigure and release the Radio

Bearer Services. The radio interface consists of three protocol layers – the physical

layer (L1), the data link layer (L2) and the network layer (L3). L2 contains the following sublayers:

Medium Access Control (MAC), Radio Link Control (RLC), Packet Data

Convergence Protocol (PDCP) and Broadcast/Multicast Control (BMC). RLC is

divided into C-plane and U-plane, while PDCP and BMC exist only in the U-plane.

L3 consists of one protocol, denoted as Radio Resource Control (RRC), which

belongs to the C-plane.

Each block represents an instance of the corresponding protocol.

The dashed lines represent the control interfaces through which the RRC protocol

controls and configures the lower layers. The SAPs between the MAC and physical

layers and between the RLC and MAC sub-layers provide the Transport Channels

(TrCHs) and the Logical Channels (LoCHs), respectively. The TrCHs are specified

for data transport between the physical layer and L2 peer entities, whereas LoCHs

just define the transfer of a specific type of information over the radio interface

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The dedicated higher layer information, including user data and signalling, is carried

by the uplink DPDCH, and the control information generated at L1 is mapped onto the

uplink DPCCH. The DPCCH comprises pre-defined Pilot symbols (used for channel

estimation and coherent detection/averaging), power control commands, Feedback

Information (FBI) for closed-loop mode transmit diversity and Site Selection Diversity

Technique (SSDT), and optionally a TFCI.

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Transport Format Combination Indicator (TFCI)

for several simultaneous services. Informs the rx of the transport format combination of the transport channels mapped to DPDCH

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The common uplink physical channels are the PRACH and the PCPCH, which are

used to carry RACH and CPCH, respectively. The RACH is transmitted using open-

loop power control. The CPCH is transmitted using inner-loop power control and is

always associated with a downlink DPCCH carrying power control commands.

Physical Random Access Channel (PRACH)

Random access transmission is based on a slotted ALOHA approach with fast

acquisition indication. There are 15 access slots per two frames spaced 5120 chips

apart Information concerning which access slots are available in the cell for random

access transmission is broadcast on the BCH.

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The TCHs can be described as:

. Dedicated Traffic Channel (DTCH), a point-to-point channel dedicated to one

UE for transfer of user information (a DTCH can exist in both uplink and

downlink directions).

. Common Traffic Channel (CTCH), a point-to-multi-point unidirectional channel for

transfer of dedicated user information for all or a group of specified UEs.

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BCCH Broadcast Control Channel

BCH Broadcast Channel

CCCH Common Control Channel

CCH Control Channel

CPCH Common Packet Channel

CTCH Common Traffic Channel

DCCH Dedicated Control Channel

DCH Dedicated Channel

DSCH Downlink Shared Channel

DTCH Dedicated Traffic Channel

FACH Forward Access Channel

HS-DSCH High Speed DSCH

PCCH Paging Control Channel

PCH Paging Channel

RACH Random Access Channel

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The link performance requirements are different for different services, for example,

because of different channel-coding schemes and interleaving depths. Assumptions

regarding the radio propagation channel must be carefully chosen, as the propagation

channel has a significant effect on the link performance indicators. Also the speed of

the UE must be taken into account.

In reality, channel conditions vary from cell to cell and even within cells. Thus,

choosing a specific multi-path channel model, as is usually done in simulations, is

not ideal. However, it is the only way to ensure consistency when comparing issues

in the development phase, such as the performance of different receiver algorithms or

of different network-level radio resource management algorithms, or even different approaches in cell deployment.

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Block Error Rate (BLER)

BLER is the long-term average block error rate calculated for TBs. The TB is considered erroneous if it has at least one bit error. The system knows the correctness of the blocks with very high reliability through the CRC.

Bit Error Rate (BER)

BER refers here to the information bit error rate – i.e., for user bits after decoding. The

BER of channel-coded bits is always higher.

Bit Rate, R

The bit rate, R, used in link-level simulations refers to user information bits. This means that the overhead from L1, such as CRC bits, coding and DPCCH control bits, is added in the simulations, but this only increases the energy required to transport the information bits over the air with the required quality (BER, BLER) for the information bits.

Eb/No and Orthogonality

Originally, Eb/No meant simply bit energy divided by noise spectral density. However, over time the expression ‘Eb/No’ has acquired an additional meaning. One reason is the fact that in CDMA the interference spectral density is added to the noise spectral density, since the interference is noiselike, due to the spreading operation.

Ec/Io

Ec/Io is the received chip energy relative to the total power spectral density. In the uplink this is the same as Eb/No divided by the processing gain – i.e., by W=R. In the downlink Io is the total received power spectral density, thus the orthogonality effects are not taken into account.

Ec/Ior

Ec/Ior is the transmitted energy per chip on a chosen channel relative to the total transmitted power spectral density at the BS. Notice that it is also the fraction of thepower allocated to the channel from the total BS transmitted power used.

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Average Power Rise

It is measured from the link-level simulations as the difference between the average transmitted power and the average received power, with the condition that the average channel gain is 1. In the uplink, the power rise effectively only increases the interference received from surrounding cells, and in dimensioning it is added during the interference calculation. In the downlink the average power rise is included in the basic Eb/No figures.

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