31-12-2009, 06:35 PM
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ABSTRACT
Currently, almost all network operators worldwide are upgrading their GSM networks in order to provide high speed mobile data to their subscribers. The ever increasing growth rate of data applications such as e-mail and the internet is confronting mobile network operators worldwide with the challenge to upgrade their networks to high bandwidth capable "bit pipes" in order to provide for all kinds of mobile data applications. High speed mobile data will combine two of today's most rapidly growing technologies, mobility and the internet.
GPRS (General Packet Radio Service), EDGE (Enhanced Data rates for Global Evolution) and HSCSD (High Speed Circuit Switched Data) have been designed primarily as upgrades to the well known and widely used GSM standard. In the 1980s and early 1990s, when the GSM system was designed and standardized, data transmission capabilities were of minor importance compared to voice. Besides, at that time, the maximum transmission speed of 9.6 kbit/s that GSM offered, appeared to be sufficient and was comparable with analog wireline modems.
Starting with HSCSD, the first high speed mobile data upgrade to be standardized, higher rates of transmission can be provided to mobile customers. EDGE has a transmission speed of up to 384 kbit/s and GPRS is able to support up to 160 kbit/s.
INTRODUCTION
Currently, almost all network operators worldwide are upgrading their GSM networks in order to provide high speed mobile data to their subscribers. This subclause focuses on providing you with an overview of some typical applications for high speed mobile data. We also would like to make you aware of some of the general advantages and risks. When are HSCSD and EDGE available for commercial applications? What are some of the general aspects that all high speed mobile data options have in common?
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THE NEED FOR HIGH SPEED MOBILE DATA
Why High Speed Mobile Data?
The ever increasing growth rate of data applications such as e-mail and the internet is confronting mobile network operators worldwide with the challenge to upgrade their networks to high bandwidth capable "bit pipes" in order to provide for all kinds of mobile data applications. High speed mobile data will combine two of today's most rapidly growing technologies, mobility and the internet.
Let us compare the situation on the mobile side with the progress that has been made on the fixed end. While even today's analog modems operate at 56 kbit/s and, indeed, ISDN transmits up to 128 kbit/s, mobile users are still limited to 9.6 kbit/s in of GSM. The rollout of XDSL improves the situation even further on the wireline side, thereby broadening the gap between wireline and wireless.
Bandwidth Requirements
The figure below presents the bandwidth requirements for some typical data transfer applications. Note that these requirements apply to both wireline and mobile usage. Obviously, GSM can barely cope with surfing the web and video-conferencing is totally unfeasible.
Customer Potential
With regard to mobile data, not just the typical pattern of use by today's businessmen on the move shall be addressed: Today's GSM-networks are also used by many consumers for the largest growing mobile data application of the late 1990's, SMS. Therefore, the new mobile data technologies need to address both consumer groups, the private customer and the business user. In the first instance, most network operators intend to attract their high-end business subscribers, their long term goal being, however, to bring high speed mobile data to the mass market.
High Speed Data Options for GSM
The figure below illustrates the evolution of data services in GSM. Please note that packet-switched services are illustrated in red while circuit-switched services are shown in blue. The following sections will provide a technical introduction to these new services.
AN HISTORICAL VIEW
GPRS (General Packet Radio Service), EDGE (Enhanced Data rates for Global Evolution) and HSCSD (High Speed Circuit Switched Data) have been designed primarily as upgrades to the well known and widely used GSM standard. In the 1980s and early 1990s, when the GSM system was designed and standardized, data transmission capabilities were of minor importance compared to voice. Besides, at that time, the maximum transmission speed of 9.6 kbit/s that GSM offered, appeared to be sufficient and was comparable with analog wireline modems.
Starting with HSCSD, the first high speed mobile data upgrade to be standardized, higher rates of transmission can be provided to mobile customers. EDGE has a transmission speed of up to 384 kbit/s and GPRS is able to support up to 160 kbit/s.
THE APPLICATION PERSPECTIVE
Applications for High Speed Mobile Data
Today, many business and marketing experts worldwide are seeking the ultimate "killer application" to justify the huge investments in high speed data upgrades and 3G-technology. People generally focus on e-mail, file transfer and accessing the WWW for the usual internet transactions when considering applications for high speed mobile data. These applications will, of course, be important but there will also be new applicatons which will suit the specific needs of mobile usage. Despite this, many new applications will only come into being when the mobile networks have been upgraded. For those applications, the mobile device, as we know it, will not be deployed. However, even today, entirely new mobile data applications that do not involve the common mobile user or usage are already emerging. Let us examine a few of these applications.
TELEMETRIC APPLICATIONS
Beverage or snack machines may be equipped with high speed mobile data devices in order to transmit the remaining level of stock. Thus, time-consuming and expensive "drive-ins" will only be carried out when necessary. What is more, the customer will always find his/her preferred choice. With the advent of high-speed mobile data and an underlying IP protocol stack, the internet and packet-switched transmission can be used to transfer telemetric information. This will keep prices low and makes telemetric applications available to a wide range of new customers.
TOLL ROAD SERVICES
Nowadays, tolls are generally collected in a time-consuming and, hence, costly fashion. In the future of high speed mobile data, cars may be equipped with a mobile data device and rechargeable electronic cash in order to pay the toll by merely passing through the toll station. Again, the underlying IP protocol stack and the use of the internet will make this application cheap and reliable.
Surveillance Cameras:
Another interesting application for high speed mobile data is a webcam-based surveillance of homes or people. For instance, one can keep an eye on the household whilst on vacation or watch the children whilst they are at playschool. The installation of these cameras is simple because they are wireless devices and their operation is even simpler because the network connectivity is provided via the internet.
Advantages of High Speed Mobile Data:
Some of the aforementioned applications have already been evaluated and some have indeed been implemented using the existing wireless infrastructure. However, in most cases, the technicians were faced with the unresolvable issue of connectivity. In other cases, a network for providing a connection was available but simply was not designed for data applications. These required the development of an entirely new protocol stack. With regard to the upcoming high speed mobile data services, well-known and well-understood protocol stacks such as IP may be used to develop the applications.
Focus on Applications
It will be the application side that provides the impetus to high speed mobile data. As such, an operator's decision on whether to implement GPRS, EDGE or even UMTS, should not be top priority . The services that operators intend to provide to their subscribers through their wireless high speed data channels is far more important. Indeed, the question of speed is ultimately not all too important. Most applications that people have in mind for UMTS also work well on EDGE or even GPRS. Accordingly, the commercial service of GPRS will show whether high speed mobile data pays off for operators and subscribers. If GPRS is not a success, it is highly unlikely that UMTS will be a success.
THE VALUE CHAIN TODAY AND WITH HIGH SPEED MOBILE DATA
With today's focus on speech services, it is mainly the network operators and service providers who generate their revenue from the mass mobile market. In future, there will be a third party who will enter the market: This third party consists of the content providers who will provide the applications for high speed mobile data. These applications will require all the airtime of high speed mobile data networks.
PROBLEMS OF HIGH SPEED MOBILE DATA
High speed mobile data will certainly improve the existing mobile networks greatly. GPRS and EDGE, in particular, will write a new chapter in mobile communications history. However, there are various problems which need addressing in order to make high speed mobile data a commercial success.
Firstly, who shall provide all the necessary IP-addresses when many people are permanently online? Even today, a shortage of IP addresses is becoming evident. The only solution to this issue is an upgrade to IP version 6 but the question is when IP version 6 become a reality will.
Another problem is the short span between GPRS, EDGE and UMTS. Even before the demand for GPRS has been proven, the technical evolution has already found successors to GPRS, namely EDGE and UMTS. Perhaps the market will not be ready for UMTS when it becomes available in 2002.
Most importantly, however, there is one fundamental question: Is there really a market for high speed mobile data or will GPRS, EDGE and UMTS suffer like the mobile satellite networks?
The latter is the issue which really needs to be addressed. On the one hand, the content providers need to examine this issue and on the other hand, the network and service operators need to be willing to accept changes to the value chain so that content providers can also prosper from the mobile communications market.
HSCSD
HSCSD is circuit-switched and hardly any operator decided to implement it. This subclause will provide you with an overview of HSCSD. It will describe its principles and performance and it will explain why HSCSD is the simplest high speed data upgrade for GSM.
Principles
The Principles of HSCSD:
HSCSD or High Speed Circuit Switched Data was the first upgrade to be standardized by ETSI to bring high speed data to GSM. The standardization process started as early as 1994 and therefore, HSCSD was the first high speed data extension to be ready for implementation in 1999. The basic idea behind HSCSD is to bundle more than one timeslot on the air-interface for a single connection. Applying this simple idea, HSCSD is able to reach throughput rates of up to 57.6 kbit/s. However, the real-life implementations of HSCSD barely exceed 38.4 kbit/s.
SERVICES
HSCSD Services:
HSCSD services have two distinguishing features:
¢ Symmetric / Asymmetric: Symmetric connections provide identical throughput rates in the uplink and downlink directions. Asymmetric connections have a greater throughput rate in the downlink direction. Note that HSCSD does not provide for higher throughput rates in the uplink rather than in the downlink direction .
¢ Transparent / Non-Transparent: Transparent data services do not deploy extra measures for error recognition or correction while non-transparent data services use the Radio Link Protocol (RLP) to carry out these functions.
PERFORMANCE
HSCSD Performance:
Based on timeslot bundling, HSCSD can provide speeds up to 57.6 kbit/s. However, as illustrated in the table below, its performance depends on the number of timeslots and the channel type. Note that commercial implementations of HSCSD barely exceed a speed of 38.4 kbit/s.
Data Rate Required number of
Fullrate TCHâ„¢s with 4.8 kbit/s Required number of
Fullrate TCHâ„¢s with 9.6 kbit/s Required number of
Fullrate TCHâ„¢s with 14.4 kbit/s
4.8 kbit/s 1 -/- -/-
9.6 kbit/s 2 1 -/-
14.4 kbit/s 3 -/- 1
19.2 kbit/s 4 2 -/-
28.8 kbit/s -/- 3 2
38.4 kbit/s -/- 4 -/-
43.2 kbit/s -/- -/- 3
57.6 kbit/s -/- -/- 4
The HSCSD Network Infrastructure
HSCSD is a circuit-switched technology. Therefore, one of its major advantages is that the existing core network, mainly the MSC, is able to handle HSCSD traffic. As opposed to GPRS, HSCSD neither requires a hardware upgrade within the network, nor does it introduce new channel coding technologies. Therefore, HSCSD is a rather simple upgrade of the standard GSM, particularly in comparison with GPRS and EDGE. When HSCSD is added to an existing network, it is mainly the interworking functions within the MSC and, of course, the mobile stations that are affected. All other network elements and protocols remain transparent with HSCSD.
GPRS
GPRS is a packet-switched upgrade to GSM. What consequences does packet-switching actually have on a mobile network? How does GPRS perform in comparison with e.g. HSCSD? How will the GSM networks need upgrading in order to implement GPRS ?
Principles
GPRS is Packet-Switched:
GPRS or General Packet Radio Service is a packet-switched technology based on GSM. As shown in the animation, the radio and network resources are only accessed when data actually needs to be transmitted between the mobile user and the network. Please note that in between alternating transmissions, no network resources need to be allocated. Compare this to the circuit-switched transaction where resources are being accessed permanently, regardless of whether or not transmission is actually talking place. Therefore, packet-switching saves resources, especially in the case of bursty transactions.
Performance
GPRS Offers Bandwidths up to 160 kbit/s With the development of HSCSD, the idea of timeslot bundling to achieve higher data rates was born. GPRS also applies timeslot bundling but additionally, new channel coding schemes have been defined. With 8 timeslots and coding scheme 4, GPRS is able to provide a net throughput rate of 160 kbit/s. However, GPRS can not change physical laws. In other words, the channel coding schemes that provide for higher data transmission rates per timeslot sacrifice data protection for speed. Therefore, the new coding schemes 2, 3 and 4 make less provision for forward error correction and can only be applied when radio conditions are good to excellent.
1 Timeslot 2 Timeslots 8 Timeslots
CS-1: 8.0 kbit/s 16.0 kbit/s 64.0 kbit/s
CS-2: 12.0 kbit/s 24.0 kbit/s 96.0 kbit/s
CS-3: 14.4 kbit/s 28.8 kbit/s 115.2 kbit/s
CS-4: 20.0 kbit/s 40.0 kbit/s 160.0 kbit/s
The GPRS Network Structure
For GPRS, the existing network switching infrastructure cannot be reused, an entirely new core network is required. However, the base station subsystem or BSS can be used for both circuit-switched services and GPRS packet-switched services. Please note that the BSS needs to be upgraded with the so-called Packet Control Unit or PCU.
The new network elements within the GPRS core network are the Serving GPRS Support Node or SGSN, the Gateway GPRS Support Node or GGSN, the Border Gateway or BG and the Charging Gateway or CG.
EDGE
EDGE will provide the highest speeds in the second generation of mobile networks. However, how can EDGE achieve these high throughput rates compared to GPRS or HSCSD? Is EDGE really the third alternative to GPRS and HSCSD with regard to high speed mobile data? If EDGE is so superior to HSCSD and GPRS, why not upgrade directly to EDGE, leaving out HSCSD and GPRS? Indeed, why is the mobile industry in the US also talking about EDGE ?
This subclause will address all these issues.
The EDGE-Family
Formerly, EDGE was the abbreviation for Enhanced Data rates for GSM Evolution. Nowadays, with EDGE also being adopted by the North American market, EDGE is the acronym for Enhanced Data rates for Global Evolution. However, EDGE is not a single standard or protocol stack for high speed mobile data. Instead, EDGE introduces a new modulation scheme which is 8-PSK in addition to, e.g. GMSK in the case of GSM. As illustrated in the figure below, three members of the EDGE family need to be distinguished. There is EDGE for GSM which will migrate GPRS and HSCSD to EGPRS and ECSD. There is also the North American EDGE extension for the IS-136 standard which is called IS-136 HS or EDGE Compact. Finally, there is UWC 136 which is the UWCC's proposal for IMT-2000.
8-PSK Modulation
GPRS and HSCSD work with the normal GSM modulation scheme which is GMSK. GMSK has a lot of advantages, the most important of which being that it does not contain any amplitude modulation. However, its inherent low speed is the one big disadvantage. In GMSK, only 1 bit can be transmitted per symbol as opposed to e.g. 8-PSK where 3 bits are transmitted per symbol. As highlighted in the animation, this makes 8-PSK three times faster than GMSK.
EDGE and Interference
Tripling the data transmission rate on the Air-Interface by applying 8-PSK seems like an obvious step forward. However, it has some inherent disadvantages, in particular, through the unpredictable environment of radio transmission. With increasing interference, the clearly distinguishable symbols of 8-PSK, as shown in the animation, become more and more diffused. At a certain stage, the receiver is no longer able to distinguish between different symbols. Obviously, 8-PSK with 8 different symbols is more vulnerable to such interference than e.g. GMSK.
Liabilities of EDGE
In a radio environment, the greater the distance between the sender and the receiver, the greater the probability of interference. The distance between sender and receiver makes up the effective cell size in a cellular mobile network. Applying EDGE with 8-PSK-modulation to such a network implies shrinking the effective cell size. This is due to the fact that 8-PSK is more vulnerable to interference which in turn increases with distance. As illustrated in the figure below, the price of the impressive transmission rate of EDGE is a smaller cell radius. In an existing mobile network, this will limit the feasibility of the implementation of EDGE to urban environments with their high concentration of users and base stations.
EDGE Requires a Major Hardware Upgrade
EDGE is mainly concerned with the modulation scheme on the Air-Interface. Adding 8-PSK as a new modulation scheme requires all base stations to receive a hardware upgrade of their RF-parts to support the EDGE technology. This is a major undertaking which is full of risk and, most importantly, is extremely costly to the operator.
CONCLUSION
High speed mobile data will certainly improve the existing mobile networks greatly. GPRS and EDGE, in particular, will write a new chapter in mobile communications history. Currently, almost all network operators worldwide are upgrading their GSM networks in order to provide high speed mobile data to their subscribers.
HSCSD is a circuit-switched technology. Therefore, one of its major advantages is that the existing core network, mainly the MSC, is able to handle HSCSD traffic. As opposed to GPRS, HSCSD neither requires a hardware upgrade within the network, nor does it introduce new channel coding technologies. Therefore, HSCSD is a rather simple upgrade of the standard GSM, particularly in comparison with GPRS and EDGE.
GPRS also applies timeslot bundling but additionally, new channel coding schemes have been defined. With 8 timeslots and coding scheme 4, GPRS is able to provide a net throughput rate of 160 kbit/s. However, GPRS can not change physical laws. In other words, the channel coding schemes that provide for higher data transmission rates per timeslot sacrifice data protection for speed.
EDGE is mainly concerned with the modulation scheme on the Air-Interface. Adding 8-PSK as a new modulation scheme requires all base stations to receive a hardware upgrade of their RF-parts to support the EDGE technology. This is a major undertaking which is full of risk and, most importantly, is extremely costly to the operator
REFERENCES
1. gsmworld.com
2. gsmdata.com
3. ericson.com
4. 3gpp.com
5. The essential guide to wireless communication --- Andy Dorman
6. The Principles of communication “ Taub & Schilling
ACKNOWLEDGMENT
I express my sincere thanks to Prof. M.N Agnisarman Namboothiri (Head of the Department, Computer Science and Engineering, MESCE), Mr. Sminesh (Staff incharge) for their kind co-operation for presenting the seminars.
I also extend my sincere thanks to all other members of the faculty of Computer Science and Engineering Department and my friends for their co-operation and encouragement.
Hafeez Rasheed
CONTENTS
¢ INTRODUCTION
¢ THE NEED FOR HIGH SPEED MOBILE DATA
¢ AN HISTORICAL VIEW
¢ THE APPLICATION PERSPECTIVE
¢ THE VALUE CHAIN TODAY AND WITH HIGH SPEED MOBILE DATA
¢ PROBLEMS OF HIGH SPEED MOBILE DATA
¢ HSCSD
¢ GPRS
¢ EDGE
¢ CONCLUSION
¢ REFERENCES
