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W-CDMAW-CDMA- Wideband "radio pipe" for 3G services
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WCDMA (Wideband Code Division Multiple Access) is the radio access technology selected by ETSI (European Telecommunications Standards Institute) in January 1998 for wideband radio access to support third-generation multimedia services.
Optimized to allow very high-speed multimedia services such as voice, Internet access and videoconferencing, the technology will provide access speeds at up to 2Mbit/s in the local area and 384kbit/s wide area access with full mobility. These higher data rates require a wide radio frequency band, which is why WCDMA with 5MHz carrier has been selected; compared with 200kHz carrier for narrowband GSM.
Easy integration into existing infrastructure. WCDMA can be added to the existing GSM core network. This will be particularly beneficial when large portions of new spectrum are made available, for example in the new paired 2GHz bands in Europe and Asia. It will also minimize the investment required for WCDMA rollout - it will, for example, be possible for existing GSM sites and equipment to be reused to a large extent.
A single standard for all.
An agreement on a globally harmonized third-generation CDMA radio standard that addresses the needs of all current wireless communities was reached by the Operators' Harmonization Group in May 1999. There will be three modes in the harmonized 3G CDMA standard; a direct-sequence mode for WCDMA, a multi-carrier mode for cdma2000 (an evolution of narrowband CDMA), and a time division duplex (TDD) CDMA mode.
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Right answer is relative to Bit Rate (Processing Gain) W/R
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3G standards nearing final hurdle Ericsson News
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Agreement on the IMT-2000 radio specifications ensures the interoperability and interworking of mobile systems. Mobile terminal manufacturers will be able to build units which work anywhere in the world regardless of local network or radio options.
The five terrestrial radio interface standards are:
 IMT DS, widely known as Wideband CDMA, or WCDMA, IMT MC, widely known as cdma2000 and consisting of the 1X and 3X components, IMT TC, called UTRA TDD or TD-SCDMA, IMT SC, called UWC-136 and widely known as EDGE, IMT FT, well-known as DECT. |
CDMA
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One important property of the air interface of a cellullar telephone system is the multiple access method. Each user of the cellular system
is given a channel, and all users get different channels. The way in which these channels are different is determined by the multiple access
method. Traditionally in a radio communication system, each channel occupies its own frequency. This is for instance the case in FM radio
broadcasting: different stations have different frequencies. By tuning the radio receiver to a specific frequency, the listener can choose
which station he or she wants to listen to. This multiple access scheme is called Frequency Division Multiple Access or FDMA. The analog
cellular systems, e.g. NMT, use FDMA.
The pan-european cellular system GSM uses Time Division Multiple Access or TDMA as its main multiple access method. In TDMA, the
channels are separated by use of time slots. Many users occupy the same frequency, but not at the same time. The mobile telephones
take turn to transmit. Typically, each time slot is a few microseconds long. TDMA is also used in the North American cellular standard
IS-54 and in the Japanese system PDC.
In a cellular system employing Direct Sequence Code Division Multiple Access (DS-CDMA), all users use the same frequency at the same
time. Before transmission, the signal from each user is multiplied by a distinct signature waveform. The signature waveform is a signal
which has a much larger bandwidth than the information bearing signal from the user. The CDMA system is thus a spread spectrum
technique. All users use different signatures waveforms to expand their signal bandwidth. The procedure is depicted below for a
two-user case. Notice the phase shifts in the transmitted signal due to the negative pulses in the data stream.
More information on http://www.signal.uu.se/Research/rmultiuser.html
What is CDMA? How does it work ?
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With CDMA, unique digital codes, rather than separate RF frequencies or channels, are used to differentiate subscribers. The codes are shared by both the mobile station (cellular phone) and the base station, and are called 'pseudo-Random Code Sequences'. All users share the same range of radio spectrum.
For cellular telephony, CDMA is a digital multiple access technique specified by the Telecommunications Industry Association (TIA) as IS-95.
IS-95 systems divide the radio spectrum into carriers which are 1,250 kHz (1.25 MHz) wide. One of the unique aspects of CDMA is that while there are certainly limits to the number of phone calls that can be handled by a carrier, this is not a fixed number. Rather, the capacity of the system will be dependent on a number of different factors.
IS-95 uses a multiple access spectrum spreading technique called Direct Sequence (DS) CDMA.
Each user is assigned a binary, Direct Sequence code during a call. The DS code is a signal generated by linear modulation with wideband Pseudorandom Noise (PN) sequences. As a result, DS CDMA uses much wider signals than those used in other technologies. Wideband signals reduce interference and allow one-cell frequency reuse.
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There is no time division, and all users use the entire carrier, all of the time.
CDMA is a spread spectrum technology, which means that it spreads the information contained in a particular signal of interest over a much greater bandwidth than the original signal. The standard data rate of a CDMA call is 9600 bits per second (9.6kilobits per second). This initial data is spread including the application of digital codes to the data bits, up to the transmitted rate of about 1.23 megabits per second. The data bits of each call are then transmitted in combination with the data bits of all the calls in the cell. At the receiving end, the digital codes are separated out, leaving only the original information that was to be communicated. At that point, each call is once again a unique data stream with a rate of 9600 bits per second.
Traditional uses of spread spectrum are in military operations. Because of the wide bandwidth of a spread spectrum signal, it is very difficult to jam, difficult to interfere with, and difficult to identify. This is in contrast to technologies using a narrower bandwidth of frequencies. Since a wideband spread spectrum signal is very hard to detect, it appears as nothing more than a slight risen the 'noise floor' or interference level. With other technologies, the power of the signal is concentrated in a narrower band, which makes it easier to detect.
In CDMA, signals are sent at the same time in the same frequency band. Signals are either selected or rejected at the receiver by recognition of a user-specific signature waveform, which is constructed from an assigned spreading code. The IS95 cellular system employs the CDMA technique. In IS95 an analog speech signal that is to be sent to a cell site is first quantized and then organized into one of a number of digital frame structures. In one frame structure, a frame of 20 milliseconds' duration consists of 192 bits. Of these 192 bits, 172 represent the speech signal itself, 12 form a cyclic redundancy check that can be used for error detection, and 8 form an encoder "tail" that allows the decoder to work properly. These bits are formed into an encoded data stream. After interleaving of the encoded data stream, bits are organized into groups of six. Each group of six bits indicates which of 64 possible waveforms to transmit. Each of the waveforms to be transmitted has a particular pattern of alternating polarities and occupies a certain portion of the radio-frequency spectrum. Before one of the waveforms is transmitted, however, it is multiplied by a code sequence of polarities that alternate at a rate of 1.2288 megahertz, spreading the bandwidth occupied by the signal and causing it to occupy (after filtering at the transmitter) about 1.23 megahertz of the radio-frequency spectrum. At the cell site one user can be selected from multiple users of the same 1.23-megahertz bandwidth by its assigned code sequence.
CDMA is sometimes referred to as spread-spectrum multiple access (SSMA), because the process of multiplying the signal by the code sequence causes the power of the transmitted signal to be spread over a larger bandwidth. Frequency management, a necessary feature of FDMA, is eliminated in CDMA. When another user wishes to use the communications channel, it is assigned a code and immediately transmits instead of being stored until a frequency slot opens.
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CDMA Modulation
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CDMA uses the terms forward and reverse channels. Base transmit equates to the forward direction, and base receive is the reverse direction
(forward is what the subscriber hears and reverse is what the subscriber speaks). Both the Forward and Reverse Traffic Channels use a similar
control structure consisting of 20 millise frames. For the system, frames can be sent at either 14400, 9600, 7200, 4800, 3600, 2400, 1800,
or 1200 bps.
For example, with a Traffic Channel operating at 9600 bps, the rate can vary from frame to frame, and can be 9600, 4800, 2400, or 1200 bps.
The receiver detects the rate of the frame and processes it at the correct rate. This technique allows the channel rate to dynamically adapt to the
speech or data activity. For speech, when a talker pauses, the transmission rate is reduced to a low rate. When the talker speaks, the system
instantaneously shifts to using a higher transmission rate. This technique decreases the interference to other CDMA signals and thus allows an
increase in system capacity.
CDMA starts with a basic data rate of 9600 bits per second. This is then spread to a transmitted bit rate, or chip rate (the transmitted bits are
called chips), of 1.2288 MHz. The spreading process applies digital codes to the data bits, which increases the data rate while adding redundancy
to the system.
The chips are transmitted using a form of QPSK (quadrature phase shift keying) modulation which has been filtered to limit the bandwidth of the
signal. This is added to the signal of all the other users in that cell. When the signal is received, the coding is removed from the desired signal,
returning it to a rate of 9600 bps. When the decoding is applied to the other users codes, there is no dispersing; The signals maintain the
1.2288MHz bandwidth. The ratio of transmitted bits or chips to data bits is the coding gain. The coding gain for the IS-95 CDMA system is 128,
or 21 dB.
The hardware installations and devices used in the communication part of the IA:
Modem, connector and hardware devices inside the IA.
More information from http://www.rad.com/networks/1998/handheld/handheld.htm#The OSI Seven Layer Model
Reality
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Voice and data impose different requirements, optimally achieved by different solutions. Voice and data can coexist with some compromise in efficiency." ALL BITS ARE NOT CREATED EQUAL "
In direct sequence spreading, a very fast binary bit stream is used to shift the phase of an RF carrier. This binary stream is designed to
appear random (with equal numbers of 1's and 0's) but is generated by a digital circuit. This binary sequence can be duplicated at the
receiver and both receiver and transmitter must be synchronised for transmission. These sequences are called Pseudo Noise or PN-codes.
A pn-code is a sequence existing of chips valued at -1 and 1 (polar) or 0and 1 (non-polar).
Such bit-sequences have noise-like properties like spectral flatness and low cross and auto correlation values, and thus complicate jamming
or detection by non-target receivers.
Phase shifting is usually done by in a balanced mixer that typically shifts the RF carrier between 0 and 180 degrees - this is called binary
phase-shift keying (BPSK).
The digital information is mix with the PN-code, causing the PN-code to be inverted for a 1 bit and left unchanged for a 0 bit. The resulting
PN-code is mixed with the RF carrier to produce the spread signal.
There are several families of binary pn-codesexist: m-sequences, Gold-codes and Kasami-codes where the latter two can be created by
combining a number of selected m-sequences. The usual way of creating a pn-code is by means of shift-registers with feed-back taps.
The 3GPP system is referred to the next generation replacement for PDC in Japan and for GSM in many parts of the world. The one
unique feature of 3GPP W-CDMA is that it requires no special synchronization between cells. This unsynchronized nature makes
placing base stations in underground subways, in tunnels and inside buildings much simpler.
The 3GPP network is designed to work with the following two networks:
 MAP network: GSM NetworkANSI-41 network: U.S. Standard3GPP W-CDMA has the following benefits:
Higher capacity-2 times of IS-95, and 7 times of GSMHigh speed data rates up to 384kbps while movingUp to 2Mbps throughput for fixed applicationsWider bandwidth of 5MHz is more immune to fadingAccurate BS Synchronization not neededSupport for handoffs to and from GSM
The downlink physical channels can be described as below:
Wireless operators around the globe are launching or preparing to launch packet data services over mobile networks.
Deploying packet data is a cost-effective way for mobile carriers to balance the network resources required to
sufficiently meet the needs of the growing market for voice services and the potentially large mobile data market.
The path to high-speed packet data differs greatly, however, between GSM and cdmaOne networks. GSM operators
require a new data backbone, base station upgrades and new handsets to offer packet data services. Packet data
in cdmaOne networks is standard and was built into the IS-95 standard from its inception. All cdmaOne handsets and
base stations are packet data capable today, and the networks utilize standard Internet protocol (IP) based equipment.
GSM is circuit- based, requiring a new packet data backbone and new handsets, the commercial launch of which has
been delayed until early 2001.
In order to take advantage of higher speed packet data, the GSM and cdmaOne upgrade paths include higher speed
handsets, which will be commercially available within the next 12 to 18 months. The next major upgrade for GSM is
GPRS which is 2.5G, while the next major upgrade for cdmaOne is 1X, which is 3G. We will examine some of the critical
factors affecting an operator's ability to migrate to higher speed services and to implement a packet backbone. One
of the most critical factors is the forward and backward compatibility of the handsets--the capability of an older
handset to operate on an upgraded network and the capability of a newer handset to operate on an older network.
The commercial availability of the packet capable handsets is the second crucial factor. The Second factor is the cost
and ease of integration of the packet data network and the ability for third parties to implement services on these
data backbones to offer high-speed Internet services.
Defining the market
Currently, mobile data rates are low on both GSM at 9.6 kbps with Circuit Switched Data and cdmaOne 95A networks
at 14.4 kbps in either circuit or packet switched modes. These speeds are far lower than those available to a typical
user of a PSTN wire-line network. However, we are now entering a period that will see new and faster non-voice
mobile services. For example, anticipating an increased demand for data services, Korean and Japanese operators
SK Telecom, Hansol, DDI and IDO have already implemented commercial cdmaOne 95B packet data at speeds of 64 kbps.
The GSM data evolution path will always require new network infrastructure and new phones. Every one of the
future GSM data services from GPRS to EDGE to WCDMA (and High Speed Circuit Switched Data and Wireless
Application Protocol) requires the purchase of a new mobile phone to take full advantage of the enhanced functionality,
but all handsets will still be able to operate on the GSM network, allowing voice and CSD at 9.6Kbps. The GSM roadmap
for handsets is not forward and backward compatible. This means that GPRS handsets will not work on EDGE or 3G CDMA
DS base stations. A GSM carrier must make new investments in base stations for GPRS, EDGE and 3G CDMA DS, while
the packet backbone may only need minor modifications after deploying GPRS. GSM also requires the implementation of
IP based network elements to allow a packet overlay onto a circuit switched network. The links between the existing
GSM network infrastructure entities and the IP backbone are comprised of proprietary hardware such as the Gateway
GPRS Service Nodes (GGSNs) that link the Internet to the IP backbone. These are MODIFIED IP routers.
Using standard IP routers would have given network operators and corporate customers vendor choice, interoperability,
economies of scale with existing purchasing patterns and the like. The biggest issue with GGSNs is that new pieces of
equipment raise security concerns with IT departments. This can hinder the deployment of a mobile data application due
to the need for integration and testing. Since network operators are interested in the data traffic, this barrier to the sale
presents a challenge for the corporate work force. Discussions with suppliers of both standard IP routers and GGSNs have
indicated that a GGSN will typically cost three to four times more than the equivalent IP router, presenting another sales
barrier. Network operators are likely to subsidize the GGSN element- perhaps even giving it away free of charge with a
minimum number of GPRS phone sales.
The use of the proprietary GGSNs in the GPRS solution also has other cost implications for network operators and third
party developers. GGSNs will not realize the same economies of scale of the Internet network elements that the cdmaOne
solution does. Corporations all over the world are implementing standard routers in their corporate landline Intranets and
for standard Internet access. IT departments are building knowledge and skills with standard IP network equipment. The
addition of a new version of a router -GGSNs-- will require IT employees to learn new non-standard router configurations
specific to each GGSN vendor. We believe that this will hinder the implementation of GPRS in corporate environments.
The cdmaOne packet data implementation, on the other hand, utilizes standard routers, which are the same ones used in
the landline Internet. The same IT professionals working on a corporate landline Intranet could transfer the same skills to
a mobile Intranet based on cdmaOne. This will result in greater revenues for operators and lower costs for corporations.
Operators will not need to be integral in developing every application that is used on its network, and corporations will
require fewer resources to develop applications.
GPRS will also eventually require Mobile IP in order to offer full mobility within the Internet. Without Mobile IP, the GPRS
network will not be able to identify a node such as a portable computer that has a standard IP address. For example, GPRS
subscribers with portable computers will not be able to log into a corporate network using GPRS alone. The GPRS network
will require Mobile IP to allow the corporate network to authenticate the IP address of the portable computer. Since Mobile
IP requires more network resources, this may lead to a reduction in the volume of data available on each packet as the
transport layer information increases. The implication is that GPRS networks will be less efficient than cdmaOne networks.
cdmaOne uses Mobile IP as its transport layer.
cdmaOne is based on IP standards, giving it an inherent advantage over GPRS. Current cdmaOne phones have the standard
IP protocols built into the handset, and cdmaOne networks use IP addressing within the network without the need for an
additional IP layer being added to the packet transport layer. This allows for a high degree of backward and forward hardware
compatibility for network operators looking to implement new higher speed data services and evolve to 3G, which is an
IP-based standard.
Today's cdmaOne networks already incorporate an IP gateway referred to as the Inter-Working Function (IWF). This is essentially
a standard IP router built into the network, routing IP packets without the need for them to be handled by an analog modem.
The IWF receives information from the mobile phone in Point to Point Protocol (PPP) format and assigns a temporary IP address
for that session. Experts estimate the cost for rolling out a full network upgrade for 45 million POPS from GSM to GPRS is about
US $125 million. Adding packet data to a CDMA network is far less expensive: less than $5 million dollars. cdmaOne phones
and base stations already have IP protocols built in.
Having the IP gateway as a standard feature NOW therefore represents a significant advantage to cdmaOne network operators.
The cdmaOne configuration is based on existing corporate infrastructure standards. Certain network infrastructure manufacturers
have stated that their new cdmaOne infrastructure allows the incorporation of ANY standard router from any manufacturer into
the IWF. A standard RADIUS server undertakes billing information and authentication in the network, and messaging is handled
using SMTP. Integrating high speed cdmaOne data in a corporate network will be much easier than with GPRS, as the infrastructure
of cdmaOne is based on what is considered to be standard corporate infrastructure components. Since there is backward and
forward compatibility in the cdmaOne handsets, any handset can operate on any cdmaOne network, (assuming the same frequency
or the use of multi-band phones) of that cdmaOne network (95A, 95B or 1X) at the highest available speed possible by both the
handset and network. For example, 1X handset will be capable of 14.4 Kbps on a 95A network and 64 Kbps on a 95B network. A
95A handset will operate on a 95A, 95B or a 1X network, but only at 14.4Kbps
 * Across the raw air link; assumes 8 concatenated channels. With GPRS, the figures also assume no error correction on data transferred.
^ Indicates initial/ current support (4 slots for GPRS)
" The typical data rate available to an individual user
We can see from this analysis that the maximum theoretical speeds available over GPRS are in fact higher than 95B but less than 1x-but
in initial commercial implementations we expect 95B to outperform GPRS. KT Freetel, and Hansol in Korea, commercially launched 95B
in 1999 while DDI and IDO of Japan launched commercial service in 2000. Several, but not all, of the GPRS network infrastructure vendors
are planning to support the maximum eight channels in their technical implementations. GPRS has a disadvantage in that the initial GPRS
capable mobile terminals are expected to support only a maximum of four simultaneous channels. GPRS and voice both use the same traffic
channels, meaning that that both voice and data are competing for the same resource. Network operators, wherever they are in the world,
are reluctant to dedicate channels or assign priority to data over voice. Because of real world limitations the typical bandwidth available to
a GPRS user is expected to be less than 30 kbps, similar to the wire-line data transfer rates in 1999 and below today's 95B.
EDGE has a maximum theoretical data rate of 384 kbps, but EDGE works in a similar way to GPRS in that this would require all 8 timeslots-
which is unlikely-- to be available to a single user who would also need to be given priority over voice. As such, the theoretical maximum is
once again an irrelevant figure to an end user. We expect uses to get 114 kbps data rates.
We estimate that CDMA 1X will allow approximately 90% throughput of the implemented bandwidth to the application layer and therefore
offers a typical user rate of 130 kbps, five times the typical data rate available to a GPRS user. It should be noted that the144 kbps rate is
symmetrical.
Summary
From this analysis, we can see that the packet data design that is standardized in the network and handsets of the cdmaOne standards
technology facilitates easier and therefore less expensive packet data implementation than GPRS from a network operator, handset,
application developer and corporation's point of view. All cdmaOne handsets are packet data capable and work on all implementations
of cdmaOne networks. Phones do however remain a significant barrier to the widespread uptake of higher speed data services on both
GSM and CDMA networks.
Prepared by Warren Carley and Simon Buckingham
Mobile Lifestreams Limited
9 The Broadway
Newbury, Berkshire
RG14 1AS, UK
Tel +44 7000 366366
Fax +44 7000 366367
www.mobilelifestreams.com
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