Basic Concepts of Modulation

Modulation is the process of facilitating the transfer of information over a medium. Sound transmission in air has limited range for the amount of power your lungs can generate. To extend the range your voice can reach, we need to transmit it through a medium other than air, such as a phone line or radio. The process of converting information (ex. voice) so that it can be successfully sent through a medium (wire or radio waves) is called modulation. There are three basic types of digital modulation techniques.

• Amplitude-Shift Keying (ASK)
• Frequency-Shift Keying (FSK)
• Phase-Shift Keying (PSK)

All of these techniques vary a  parameter of sinusoid to represent the information which we wish to send. A sinusoid has three different parameters that can be varied. These are amplitude, phase and frequency. Modulation is a process of mapping such that it takes your voice (as an example of signal) converts it into some aspect of sine wave and then transmits the sine wave, leaving the actual voice behind. The sine wave on the other side is remapped back to a near copy of your sound.

The medium is the thing through which the sine wave travels. So wire is a medium and so are air, water and space. The sine wave is called carrier. The information to be sent, which can be voice or data is called the information signal. Once the carrier is mapped with the information to be sent, it is no longer a sine wave and we call it the signal. The signal has the unfortunate luck of getting corrupted by noise as it travels.

In ASK, the amplitude of the carrier is changed in response to information and all else is kept fixed. Bit 1 is transmitted by a carrier of one particular amplitude. To transmit 0, we change the amplitude keeping the frequency constant. On-Off Keying (OOK) is a special form of ASK, where one of the amplitude is zero.

In FSK, we change the frequency in response to information, one particular frequency for a 1 and another frequency for a 0.

In PSK, we change the phase of the sinusoidal carrier to indicate information. Phase in this context is the starting angle at which the sinusoid starts. To transmit 0, we shift the phase of the sinusoid by 180°. Phase shift represents the change in the state of the information in this case.

ASK techniques are the most susceptible to the effects of non-linear devices which compress and distort signal amplitude. To avoid such distortion, the system must be operated in the linear range, away from the point of maximum power where most of the non-linear behavior occurs. Despite this problem in high frequency carrier systems, Amplitude Shift Keying is often used in wire-based radio signaling, both with or without a carrier.

ASK is also combined with PSK to create hybrid systems such as a Quadrature Amplitude Modulation (QAM) where both the amplitude and the phase are changed at the same time.

What is EP NO

For acquiring an AT signal on reverse link (during connection setup), RN needs to know the approximate distance from the antenna. RN uses this distance and a BTS wide search window configurable value to search the signal from AT. This distance is known as Earliest PN Offset (EPNO).

Walsh Codes

Walsh Code is a group of spreading codes having good autocorrelation properties and poor crosscorrelation properties. Walsh codes are the backbone of CDMA systems and are used to develop the individual channels in CDMA.

For IS-95, 64 codes are available. Code 0 is used as the pilot and code 32 is used for synchronization. Codes 1 though 7 are used for control channels, and the remaining codes are available for traffic channels. Codes 2 through 7 are also available for traffic channels if they are not needed. For cdma2000, there exists a multitude of Walsh codes that vary in length to accommodate the different data rates and Spreading Factors of the different Radio Configurations.

IS-95 uses 64 Walsh codes and these allow the creation of 64 channels the base station. In other words, a base station can talk to a maximum of 64 (this number is actually only 54 because some codes are used for pilot and synch channels) mobiles at the same time. CDMA 2000 used 256 of these codes.

Walsh codes are created out of Haddamard matrices and Transform. Haddamard is the matrix type from which Walsh created these codes. Walsh codes have just one outstanding quality. In a family of Walsh codes, all codes are orthogonal to each other and are used to create channelization within the 1.25 MHz band.

Here are first four Hadamard matrices. The code length is the size of the matrix. Each
row is one Walsh code of size N. The first matrix gives us two codes; 00, 01. The second
matrix gives: 0000, 0101, 0011, 0110 and so on.

Their main purpose of Walsh codes in CDMA is to provide orthogonality among all the users in a cell. Each user traffic channel is assigned a different Walsh code by the base station. IS-95 has capability to use 64 codes, whereas CDMA 2000 can use up to 256 such codes. They are also used to create an orthogonal modulation on the forward link and are used for modulation and spreading on the reverse channel.

Orthogonal means that cross correlation between Walsh codes is zero when aligned. However, the auto-correlation of Walsh-Hadamard codewords does not have good characteristics. It can have more than one peak and this makes it difficult for the receiver to detect the beginning of the codeword without an external synchronization. The partial sequence cross correlation can also be non-zero and un-synchronized users can interfere with each other particularly as the multipath environment will differentially delay the sequences. This is why Walsh-Hadamard codes are only used in synchronous CDMA and only by the base station which can maintain orthogonality between signals for its users.

The above is simplified look at the use of these codes. Assume there are three users in
one cell. Each is trying to talk to someone else. User 1 wants to talk to someone who is
outside its cell and is in cell 2. User 3 wants to talk to someone in cell 3.

Let’s take User 1. Its data is first covered by a channel Wash code, which is any Walsh code from 8 to 63. It is assigned to the user by the base station 1 in whose cell the mobile is located. The Base Station has also assigned different Walsh codes to users 2 and 3. All three of these are different are assigned by base station 1 and are orthogonal to each other. This keeps the data apart at the base station. Now based on the random number assigned by the BS, the mobile generates a long code mask (which is just the starting point of the long code sequence and is a scalar number). It now multiplies the signal by this long code starting at the mask ID. Now it multiplies it by the short code of the base station to whom it is directing the signal.

When the base station receives this signal, it can read the long code and see that the message needs to be routed to base station 2. So it strips off 1st short code and adds on the short code of base station 2 which is then broadcast by the BS 1 to BS 2 or sent by landlines. BS2 then broadcasts this signal along to all mobiles in its cell. The users who is located in this cell, now does the reverse. It multiplies the signal by the BS 2 short code (it knows nothing about BS 1 where the message generated) then it multiplies the signal by the same long code as the generating mobile. How? During the call paging, the mobile was given the same random number from which it creates the same long code mask. After that it multiplies it by the Walsh code sequence (also relayed during call setup).

Spread Spectrum Signals - CDMA

Spread Spectrum uses wide band, noise-like signals. Because Spread Spectrum signals are noise-like, they are hard to detect. Spread Spectrum signals are also hard to Intercept or demodulate. Further, Spread Spectrum signals are harder to jam (interfere with) than narrowband signals. These Low Probability of Intercept (LPI) and anti-jam (AJ) features are why the military has used Spread Spectrum for so many years. Spread signals are intentionally made to be much wider band than the information they are carrying to make them more noise-like.

Spread Spectrum signals use fast codes that run many times the information bandwidth or data rate. These special "Spreading" codes are called "Pseudo Random" or "Pseudo Noise" codes. They are called "Pseudo" because they are not real gaussian noise.

Spread Spectrum transmitters uses similar transmit power levels to narrow band transmitters. Because Spread Spectrum signals are so wide, they transmit at a much lower spectral power density, measured in Watts per Hertz, than narrowband transmitters. This lower transmitted power density characteristic gives spread signals a big plus. Spread and narrow band signals can occupy the same band, with little or no interference. This capability is the main reason for all the interest in Spread Spectrum today.

Since the development of CDMA technology there has been many new releases and platforms. The original CDMA is now referred to as CDMAone. Several different variants of CDMA technology been developed continuously improving quality and data transfer speeds. Third generation CDMA technology, commonly referred to as CDMA2000 encompasses a wide variety of different standards, each continually improving upon the first including; 1X EV, 1XEV-DO, and MC 3X. CDMA2000 is the current standard used by most US carriers today. The first release of CDMA2000 was refereed to as either 3G1X, 1XRTT, or X.Designed to provide data transmissions of ten times faster then the previous technology and double the voice capacity of CDMAone.

Depending on the phone you have and its capabilities you will notice symbols in the default screen of your phone reading either 1X, 1XEV-DO or some variation of the two. This symbol defines the CDMA2000 standards your phone is operating on. Newer phones will display EV or EV-DO using the newer faster, more reliable CDMA technology.

Qualcomm the original developer of CDMA owns patents of this technology. They have granted royalty-bearing licenses to over 100 network operators.

PN Offset in CDMA

Offset is one of the 512 short code sequences used to differentiate sectors on base stations for communication with mobile units. PN stands for pseudo random noise that appears in a repetitive manner. The PN sequence forms a “short” code that is 32,768 chips in length and repeats every 26.666 milliseconds. This short code is combined with the data and transmitted in each of the forward channels. 512 points within the sequence have been selected as the PN offsets (from 0-511). Each base station uses a different point in the sequence to create a unique PN offset or identifier in its pilot signal which can be used to identify the base station sector.

For CDMA networks, the most common form of interference is pilot pollution. Each base-station sector is assigned an identifier called a PN offset, which is a timing offset based on the GPS even-second clock. Since each base station assigned to a particular frequency carrier operates at the same center frequency, the PN offset is used to distinguish base stations from one another.

When a CDMA phone searches for the strongest base-station signal, it identifies the PN offset of each signal it receives. It only looks for PNs for which the network tells it to search. This list of PNs, the neighbor list, constantly is changing since it depends on the phone's current location. Pilot pollution occurs when the CDMA mobile phone's rake receiver receives more than three (four for newer phones) pilot signals having approximately the same Ec/Io relative power levels.

Each base station sector in a cdmaOne network may transmit on the same frequency, using the same group of 64 Walsh codes for pilot, paging, sync and forward traffic channels. Therefore, another layer of coding is required so that a mobile phone can differentiate one sector from another.

The PN offset plays a key role in this code layer. The abbreviation “PN” stands for pseudo-random noise – a long bit sequence that appears to be random when viewed over a given period of time, but in fact is repetitive. In cdmaOne transmissions, the entire PN sequence is defined to form a short code that is 32,768 chips in length and repeats once every 0.027 seconds. The short code is exclusive OR’d with the data and transmitted in each of the forward channels (pilot, paging, sync, and traffic). Within the 32,768 chip sequence, 512 points have been chosen to provide PN offsets. Each base station transceiver uses a different point in the sequence to create a unique PN offset to the short code in its forward link data. As a result, a mobile phone can identify each base station sector by the PN offset in the received signal.

Each base station transmits a version of the long code that is shifted in time by a different multiple of the chip time. The PN offset represents the number of chip times by which a particular base station delays transmission of the long code. The cellular telephone receives the long code offset when the cellular telephone enters a cell or powers on, and stores the PN offset in a nonvolatile portion of memory.

Distance-based Location Update & RouteUpdateRadius in CDMA 1X EV-DO

• Introduction

Idle-mode mobility management in cellular systems involve location updates and paging. Idle-mode mobility is not tracked at the granularity of individual cells. Instead, it is tracked at a coarser granularity of a group of contiguous cells termed as a "location area". A location update mechanism involves the reporting of this location area information by an idle mode mobile to the network, whenever it moves from one location area to another. Because the network knows the location of the mobile only at the location area-level, when there is an incoming call for the mobile, the network needs to page the mobile in all the cells in the location area. Both the location update mechanism and paging will generate signaling load on the network, and reducing the load due to one of these would involve an increased load due to the other.

In CDMA 1X EV-DO, specified in 3GPP2 C.S0024-A v1.0 (2004), a dynamic distance-based location update mechanism is used. In this scheme, a mobile makes a location update if the distance between the BTS in which it is currently camped, and the BTS where it made its last location update is greater than a parameter called RouteUpdateRadius. This scheme provides a significant performance benefit over the static location update mechanism used in GSM/GPRS/UMTS networks. However, the distance-based mechanism does not utilize the knowledge of the direction of mobiles’ movement.

• 1X EV-DO Route Update Protocol

In CDMA 1X EV-DO, the idle-mode mobility management procedures are handled by the route update protocol, and it uses the distance-based location update approach. In 1X EV-DO, each cell broadcasts its latitude, longitude, and a parameter called RouteUpdateRadius. An idle mode mobile as it moves from cell to cell, monitors these three parameters. after each cell change, the mobile computes the distance between the site locations of the current cell and the cell in which it last sent a location update message. If this distance is greater than the RouteUpdateRadius parameter broadcast in the cell in which it last sent a location update message, the mobile sends another update to the network.

Otherwise mobile does not send a location update message. To perform this operation, the mobile would have to store the latitude, longitude, and RouteUpdateRadius parameters of the last cell in which it did a location update operation.

The distance computed is the distance between the site locations, and it does not depend on the location of mobile within the serving site. The latitude and longitude information is broadcasted by each cell is used for computing the distance.

Because the mobile sends a location update message only after it moves to a cell that is sufficiently far apart from the cell from which the mobile last sent a location update, the problem of ping-ponging is eliminated. Essentiall, as soon as a mobile sends a location update, it draws a circle around the serving cell of radius RouteUpdateRadius and sends the next location update only if it goes outside that circle. Clearly, this approach eliminates the ping-ponging problem of the static location area approach.

CDMA Introduction

Code Division Multiple Access (CDMA) has gained widespread international acceptance by cellular radio system operators as an upgrade that will dramatically increase both their system capacity and the service quality. CDMA is a "spread spectrum" technology, allowing many users to occupy the same time and frequency allocations in a given band/space. As its name implies, CDMA (Code Division Multiple Access) assigns unique codes to each communication to differentiate it from others in the same spectrum.

In a world of finite spectrum resources, CDMA enables many more people to share the airwaves at the same time than do alternative technologies. The core principle of spread spectrum is the use of noise-like carrier waves, and, as the name implies, bandwidths much wider than that required for simple point-to point communication at the same data rate.

1. INTRODUCTION

CDMA stands for Code Division Multiple Access, but was originally known as IS-95. Qualcomm was the first to created this technology and by 1993 it was adopted by the Telecommunication Industry Association. Later this technology was enhanced and refined by Ericsson.The world is demanding more from wireless communication technologies than ever before as more people around the world are subscribing to wireless. Add in exciting Third-Generation (3G) wireless data services and applications - such as wireless email, web, digital picture taking/sending, assisted-GPS position location applications, video and audio streaming and TV broadcasting - and wireless networks are doing much more than just a few years ago. This is where CDMA technology fits in. CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies, allowing more subscribers to connect at any given time, and it is the common platform on which 3G technologies are built.

The CDMA air interface is used in both 2G and 3G networks. 2G CDMA standards are branded cdmaOne and include IS-95A and IS-95B. CDMA is the foundation for 3G services: the two dominant IMT-2000 standards, CDMA2000 and WCDMA, are based on CDMA.

1.1 CDMAONE: The Family of IS-95 CDMA

Technologies cdmaOne describes a complete wireless system based on the TIA/EIA IS-95 CDMA standard, including IS-95A and IS-95B revisions. It represents the end-to-end wireless system and all the necessary specifications that govern its operation. cdmaOne provides a family of related services including cellular, PCS and fixed wireless (wireless local loop).

1.2 CDMA2000: Leading the 3G revolution

CDMA2000 represents a family of ITU-approved, IMT-2000 (3G) standards and includes CDMA2000 1X and CDMA2000 1xEV technologies. They deliver increased network capacity to meet growing demand for wireless services and high-speed data services. CDMA2000 1X was the world's first 3G technology commercially deployed (October 2000).

2. SPREAD SPECTRUM COMMUNICATIONS

CDMA is a form of Direct Sequence Spread Spectrum communications. In general, Spread Spectrum communications is distinguished by three key elements:

1. The signal occupies a bandwidth much greater than that which is necessary to send the

information. This results in many benefits, such as immunity to interference and jamming and multiuser access, which we'll discuss later on.

2. The bandwidth is spread by means of a code which is independent of the data. The independence of the code distinguishes this from standard modulation schemes in which the data modulation will always spread the spectrum somewhat.

3. The receiver synchronizes to the code to recover the data. The use of an independent code and synchronous reception allows multiple users to access the same frequency band at the same time.

In order to protect the signal, the code used is pseudo-random. It appears random, but is actually deterministic, so that the receiver can reconstruct the code for synchronous detection. This pseudo random code is also called pseudo-noise (PN).

There are three ways to spread the bandwidth of the signal:

• Frequency hopping. The signal is rapidly switched between different frequencies within the hopping bandwidth pseudo randomly, and the receiver knows before hand where to find the signal at any given time.

• Time hopping. The signal is transmitted in short bursts pseudo-randomly, and the receiver knows beforehand when to expect the burst.

• Direct sequence. The digital data is directly coded at a much higher frequency. The code is generated pseudo-randomly, the receiver knows how to generate the same code, and correlates the received signal with that code to extract the data.

What is Ec/I0

In CDMA refers to the portion of the RF signal which is usable. It's the difference between the signal strength and the noise floor.

Ec/Io (pronounced "ee-see over eye-not") is basically a measure of how well your phone can hear the tower over all the other traffic on the channel.

A reading near 0.0 is very good. You can find low readings late at night on weekdays when traffic is low. When the reading is high (-12.0 to -15.0), quality will drop and you may even lose the call.

BTS – Base Transceiver Station

The base transceiver station, or BTS, contains the equipment for transmitting and receiving radio signals (transceivers), antennas, and equipment for encrypting and decrypting communications with the base station controller (BSC). Typically a BTS have several transceivers (TRXs) which allow it to serve several different frequencies and different sectors of the cell (in the case of sectorised base stations).

A BTS is controlled by a parent BSC The BTSs are equipped with radios that are able to modulate layer 1 of interface Um; for GSM 2G+ the modulation type is GMSK, while for EDGE-enabled networks it is GMSK and 8-PSK.

Frequency hopping is often used to increase overall BTS performance; this involves the rapid switching of voice traffic between TRXs in a sector. A hopping sequence is followed by the TRXs and handsets using the sector. Several hopping sequences are available, and the sequence in use for a particular cell is continually broadcast by that cell so that it is known to the handsets. A TRX transmits and receives according to the GSM/CDMA standards.

In short BTS

1. Encodes,encrypts,multiplexes,modulates and feeds the RF signals to the antenna.
2. Frequency hopping
3. Communicates with Mobile station and BSC
4. Consists of Transceivers (TRX) units

Fast handoff

Fast handoff is a particular type of hard handoff that applies only to packet data sessions. Fast handoff allows the target PDSN to connect to an anchor PDSN where the packet data session was first established, eliminating the need to re-establish a PPP session while the packet data session is active. Fast handoff allows for early establishment of the A10 connections on the target side.

Dormant Handoff

A handoff that occurs when an MS with a dormant packet session determines that it has crossed a packet zone boundary. Dormant handoff results in A10 connection(s) being established between the target PCF and the target PDSN. A dormant handoff may require exchange of higher layer protocol messages between the MS and the PDSN, and thus, reactivation of the packet data session. Note that no air interface channels are handed off or re-configured as the result of a dormant handoff.

Handover Basics

Although the concept of cellular handover or cellular handoff is relatively straightforward, it is not an easy process to implement in reality. The cellular network needs to decide when handover or handoff is necessary, and to which cell. Also when the handover occurs it is necessary to re-route the call to the relevant base station along with changing the communication between the mobile and the base station to a new channel. All of this needs to be undertaken without any noticeable interruption to the call. The process is quite complicated, and in early systems calls were often lost if the process did not work correctly.

Different cellular standards handle hand over / handoff in slightly different ways. Therefore for the sake of an explanation the example of the way that GSM handles handover is given.

There are a number of parameters that need to be known to determine whether a handover is required. The signal strength of the base station with which communication is being made, along with the signal strengths of the surrounding stations. Additionally the availability of channels also needs to be known. The mobile is obviously best suited to monitor the strength of the base stations, but only the cellular network knows the status of channel availability and the network makes the decision about when the handover is to take place and to which channel of which cell.

Accordingly the mobile continually monitors the signal strengths of the base stations it can hear, including the one it is currently using, and it feeds this information back. When the strength of the signal from the base station that the mobile is using starts to fall to a level where action needs to be taken the cellular network looks at the reported strength of the signals from other cells reported by the mobile. It then checks for channel availability, and if one is available it informs this new cell to reserve a channel for the incoming mobile. When ready, the current base station passes the information for the new channel to the mobile, which then makes the change. Once there the mobile sends a message on the new channel to inform the network it has arrived. If this message is successfully sent and received then the network shuts down communication with the mobile on the old channel, freeing it up for other users, and all communication takes place on the new channel.

Under some circumstances such as when one base transceiver station is nearing its capacity, the network may decide to hand some mobiles over to another base transceiver station they are receiving that has more capacity, and in this way reduce the load on the base transceiver station that is nearly running to capacity. In this way access can be opened to the maximum number of users. In fact channel usage and capacity are very important factors in the design of a cellular network.

UMTS Handover

There are following categories of handover (also referred to as handoff):

• Hard Handover
  Hard handover means that all the old radio links in the UE are removed before the new radio links are established. Hard handover can be seamless or non-seamless. Seamless hard handover means that the handover is not perceptible to the user. In practice a handover that requires a change of the carrier frequency (inter-frequency handover) is always performed as hard handover.
  
• Soft Handover
  Soft handover means that the radio links are added and removed in a way that the UE always keeps at least one radio link to the UTRAN. Soft handover is performed by means of macro diversity, which refers to the condition that several radio links are active at the same time. Normally soft handover can be used when cells operated on the same frequency are changed.
  
• Softer handover
  Softer handover is a special case of soft handover where the radio links that are added and removed belong to the same Node B (i.e. the site of co-located base stations from which several sector-cells are served. In softer handover, macro diversity with maximum ratio combining can be performed in the Node B, whereas generally in soft handover on the downlink, macro diversity with selection combining is applied.

Generally we can distinguish between intra-cell handover and inter-cell handover. For UMTS the following types of handover are specified:

The most obvious cause for performing a handover is that due to its movement a user can be served in another cell more efficiently (like less power emission, less interference). It may however also be performed for other reasons such as system load control.

Active Set is defined as the set of Node-Bs the UE is simultaneously connected to (i.e., the UTRA cells currently assigning a downlink DPCH to the UE constitute the active set).

Cells, which are not included in the active set, but are included in the CELL_INFO_LIST belong to the Monitored Set.

Cells detected by the UE, which are neither in the CELL_INFO_LIST nor in the active set belong to the Detected Set. Reporting of measurements of the detected set is only applicable to intra-frequency measurements made by UEs in CELL_DCH state.

The different types of air interface measurements are:

Intra-frequency measurements: measurements on downlink physical channels at the same frequency as the active set. A measurement object corresponds to one cell.

Inter-frequency measurements: measurements on downlink physical channels at frequencies that differ from the frequency of the active set. A measurement object corresponds to one cell.

Inter-RAT measurements: measurements on downlink physical channels belonging to another radio access technology than UTRAN, e.g. GSM. A measurement object corresponds to one cell.

Traffic volume measurements: measurements on uplink traffic volume. A measurement object corresponds to one cell.

Quality measurements: Measurements of downlink quality parameters, e.g. downlink transport block error rate. A measurement object corresponds to one transport channel in case of BLER. A measurement object corresponds to one timeslot in case of SIR (TDD only).

UE-internal measurements: Measurements of UE transmission power and UE received signal level.

UE positioning measurements: Measurements of UE position.The UE supports a number of measurements running in parallel. The UE also supports that each measurement is controlled and reported independently of every other measurement.

DSCH - Downlink Shared Channel

The Downlink Shared Channel is a downlink transport channel that may be shared by several UE (User Equipment). It is used to carry dedicated control or traffic data from the SRNC/BTS (Serving Radio Network Controller). The DSCH will be associated with one or several downlink DCH (Dedicated Channel).

GSM Technology

What is GSM?

GSM (Global System for Mobile communications) is an open, digital cellular technology used for transmitting mobile voice and data services

The origins of GSM can be traced back to 1982 when the Groupe Spécial Mobile (GSM) was created by the European Conference of Postal and Telecommunications Administrations (CEPT) for the purpose of designing a pan-European mobile technology.

It is approximated that 80 percent of the world uses GSM technology when placing wireless calls, according to the GSM Association (GSMA), which represents the interests of the worldwide mobile communications industry. This amounts to nearly 3 billion global people.

GSM supports voice calls and data transfer speeds of up to 9.6 kbit/s, together with the transmission of SMS (Short Message Service).

GSM operates in the 900MHz and 1.8GHz bands in Europe and the 1.9GHz and 850MHz bands in the US. The 850MHz band is also used for GSM and 3G in Australia, Canada and many South American countries. By having harmonised spectrum across most of the globe, GSM’s international roaming capability allows users to access the same services when travelling abroad as at home. This gives consumers seamless and same number connectivity in more than 218 countries.

Terrestrial GSM networks now cover more than 80% of the world’s population. GSM satellite roaming has also extended service access to areas where terrestrial coverage is not available.

What is CDMA2000 1xEV-DO

EV-DO is a high-speed network protocol used for wireless data communications, primarily Internet access. EV-DO is considered a broadband technology like DSL or cable modem Internet services.

Certain classes of cellular phones support EV-DO. These phones may be available from various phone carriers around the world including Sprint and Verizon in the U.S. Additionally, various PCMCIA adapters and external modem hardware exists to enable laptops and handheld devices for EV-DO.

The EV-DO protocol uses asymmetric communications, allocating more bandwidth for downloads than for uploads. The original EVDO Revision 0 standard supports up to 2.4 Mbps data rates down but only 0.15 Mbps (about 150 Kbps) up.

An improved version of EV-DO called Revision A increases download speeds up to 3.1 Mbps and uploads to 0.8 Mbps (800 Kbps). EV-DO providers have gradually been upgrading their equipment from Rev 0 to support Rev A.

A future version of EV-DO called Revision B (not yet widely deployed) promised to offer much higher data rates as this protocol is capable of aggregating bandwidth from multiple wireless channels. Early trials have achieved EV-DO Rev B downloads of greater than 9 Mbps.

As with many other network protocols, the theoretical maximum data rates of EV-DO are not achieved in practice. Real-world networks may run at 50% or less of the rated speeds.

CDMA2000 1x EV-DO cell phone system is a standard that has evolved from the CDMA2000 mobile phone system and it is now firmly established in many areas of the world. The letters EV-DO stand for Evolution Data Only or Data Optimised. From the title it can be seen that it is a data only mobile telecommunications standard that can be run on CDMA2000 networks.

The EV-DO cell phone system is capable of providing the full 3G data rates up to 3.1 Mbps now that release A of the standard has been issued. The first commercial CDMA2000 1xEV-DO network was deployed by SK Telecom (Korea) in January 2002.

EV-DO Basics

• EV-DO - Evolution Data Optimized
• Personal broadband wireless service for a wide range of customers, from business people to students
• Always on - - similar to DSL (wherever 3G capability is available)
• Rides on CDMA signal- 1x data capability available everywhere CDMA voice service available
• Up to 10 times the peak data rate of the next best public wireless solution - 800 - 1,000 Kbps (kilobits per second) average download speeds, comparable to DSL speeds
• Allows the user to be connected herever they are are not only for email, but for downloads, large files, photos, spreadsheets, etc.
• Advantages over WiFi:
• Always on with seamless roaming!
• Signal can travel on same cell sites as cell phones
• No 300-ft range from the cell tower or "hotspot"
• Customers can access their corporate VPN (virtual private network) anywhere they can get a cellular signal via a secure, encrypted signal
• Can download and run video clips in real time
• Can provide service to customers outside of cable-modem or DSL areas
• Relatively low cost with high capacity - allows rich web browsing and application usage
• 1xRTT: 50Kbps - 100Kbps Upload and Download (bursts to 144Kbps)
• EVDO Rev 0: 400kbps-1000kbps Download (bursts up to 2.0Mbps), 50kbps-100kbps Upload (bursts to 144Kbps)
• EVDO Rev A: 600Kbps-1,400Kbps Download (bursts to 3.1Mbps), 500Kbps-800Kbps Upload (bursts to 1.8Mbps)

What are Femtocells?

Femtocells are low-power access points that can combine mobile and Internet technologies within the home. The femtocell unit generates a personal mobile phone signal in the home and connects this to the operator’s network through the Internet. This will allow improved coverage and capacity for each user within their home.

Femtocells have an output power less than 0.1 Watt, similar to other wireless home network equipment, and will typically allow up to about 4 simultaneous calls/data sessions at any time. Mobile phones connected to a femtocell will typically operate at levels similar to other wireless phones used in the home.

Femto cells or femtocells are small cellular telecommunications base stations that can be installed in residential or business environments either as single stand-alone items or in clusters to provide improved cellular coverage within a building. It is widely known that cellular coverage, especially for data transmission where good signal strengths are needed is not as good within buildings. By using a small internal base station - femtocell (femto cell), the cellular performance can be improved along with the possible provision of additional services.

In order to link the femtocells with the main core network, the mobile backhaul scheme uses the user's DSL or other Internet link. This provides a cost effective and widely available data link for the femtocells that can be used as a standard for all applications.

There are many advantages for the deployment of femtocells to both the user and the mobile network operator. For the user, the use of a femto cell within the home enables far better coverage to be enjoyed along with the possible provision of additional services, possible cost benefits, and the use of a single number for both home and mobile applications. For the network operator, the use of femtocells provides a very cost effective means of improving coverage, along with linking users to their network, and providing additional revenue from the provision of additional services.

Although there are advantages and disadvantages to the use of femtocells, their use has many advantages for both user and network provider.

Typically, a single femtocell will deliver voice services simultaneously to at least four users within the home, while allowing many more to be connected or ‘attached’ to the cell, accessing services such as SMS. Additionally, femtocells will deliver data services to multiple users, typically at the full peak rate supported by the relevant air interface technology, currently several megabits per second and rising to tens and hundreds of megabits per second in the future. But by removing the capacity hungry indoor mobile users from the outdoor network, femtocells also in effect improve performance for consumers outside. Indeed, for each additional indoor femtocell user, system resources are freed to serve about ten outdoor users. The femtocell behaves like a normal base station in that as users enter or leave the home their voice or data services are seamlessly handed over from or to the outdoor network as required.

Subscribers benefit from perfect cellular coverage and faster mobile broadband in the home as well as a more competitive voice and data tariff. Operators get optimum cellular coverage and more mobile usage in the home and dramatically reduced operating costs especially through backhaul - their single largest OPEX - and power savings. Equally importantly the cellular operators’ capital expenditure will significantly drop because accelerating data usage means they will inevitably have to heavily invest in their outdoor network in terms of new cell sites and backhaul to meet expected demand - something femtocells do at a fraction of the cost. In fact, Paul Jacobs, Qualcomm’s CEO, recently said that the gains in throughput available to femtocell users are “equivalent to that brought by the cell phone’s shift from analogue to digital.”

Finally, as mobile operators look beyond 3G to LTE or WiMAX, femtocells offer a new, dramatically lower-cost model for network rollout. For example, LTE femtocells could be employed using higher frequencies to deliver targeted intense high bandwidth requirements inside buildings - exactly where subscribers most demand it. Operators can then use their existing networks outdoors as demand slowly builds up and then use the scarce lower frequency spectrum to provide good quality LTE coverage across entire markets with the minimum number of outdoor network cells. As we have seen, the simple proposition of lower costs, for both operators and consumers, combined with improved coverage and services is compelling. Yet there are also challenges which must be overcome before widespread commercial deployments can become a reality.