Data over Wireless - Technology Trends

A scenario in the near future:
Mr. Rao has landed in Cochin airport, with visions of spending a week in the lush green backwaters of Kerala. Once out of the airport he does not have a clue as to where to go. No problems! He whips out his state-of-the-art mobile device and logs in to his travel agent's wireless-enabled website. A quick check reveals the address of his holiday booking office. A call to the booking office ensures that he has the right address. The "local map" item which has miraculously appeared on his phone menu opens up a detailed city map which shows him the way to get there.

At the booking office Mr. Rao finds that he does not have enough money to make the booking. He smiles and logs into his bank through his mobile device. In two minutes he has transferred the requisite funds to the booking office. He is on his way! En-route he sees the swaying palms that his mother loves so much. He pulls out his digital camera and captures the image. At the click of a button a wireless link is established from the camera to his mobile device. Mr. Rao then uploads the digital image to his website and uses the mobile's keypad to e-mail his mother about the picture.

Today's Technology:
In the scenario above, Mr. Rao used his mobile device as a high end data terminal. Barring the call to the booking office (which probably used Voice over IP, a data service) the mobile device bore no resemblance to today's cell-phones.

Wireless networks in the past have been primarily used as voice bearers. But transmitting data over wireless networks is not a new concept. There have been various attempts, starting in the 1980's, to promote data transmission using mobile devices. Though the technology was always sound, the interest and corporate backing for wireless data was low-key. It is only now, when the mobile world is rapidly converging with Internet technologies, that wireless data is getting the attention it deserves. This article looks at GSM data trends, though there have been similar developments in American and Japanese (non-GSM) networks.

Short Message Service (SMS) has been available in GSM networks since 1992. It enables "short" messages of up to 160 characters to be exchanged between two users or between the network and the user. This service is implemented by adding an additional network element called the SMS Center, connected to the switch. It uses the network's signaling path and not its bearer channels. SMS has been used innovatively by operators, to provide e-mail, chat and calendar services to subscribers. However it lacks the capacity to be a bearer for high bandwidth services. Besides it uses a store-and-forward mechanism, so any kind of real-time operation is ruled out.

Circuit Switched Data (CSD) is another popular data bearer in existing GSM networks. In this system the user dials up a number to which she wants to transmit data. A dedicated connection is established via the GSM network and the user is charged for every second of connection time. The network converts the digital data received from the mobile device into analog data suitable for transmitting over normal phone lines. While this bearer supports bandwidths of 9.6 kbps and higher, it is very expensive.

Unstructured Supplementary Services Data (USSD) is gaining popularity as a bearer for GSM services. Originally introduced as a user-network dialogue mechanism for service creation, it has now been adapted to carry non-protocol data. It is similar to SMS in that it uses the signaling path of the network, and has restrictions on the size of messages it can carry. However it is a session-based service and allows users to exchange data in real-time. USSD is unique because it has built-in roaming support, so a user from Bangalore can in theory visit Madras and still receive data intended for her.

Several innovations enhance data rates on existing networks. Multi-slot capability is one such innovation. A GSM phone's bandwidth is restricted by the fact that the network allots it only one time slot to transmit its data. Multi-slot technology allows the phone to grab up to four time slots or channels and achieve higher data rates. Of course, the cost of the call is correspondingly higher. Data compression is also used to compact the data sent out and thus increase the user's effective bandwidth.

Coming up - GPRS and EDGE
The General Packet Radio System (GPRS) is set to revolutionize the way data is sent and received over wireless networks. GPRS uses packet switching, which means a circuit need not be established between two users prior to exchanging data. Network resources are optimally shared between subscribers, and used only when there is data to be sent or received by a user. Thus a user can be "always connected" to the network and pay for the volume of data sent/received as opposed to the connection duration.

GPRS is geared for data from the very start. In addition to packet switching it allows multi-slot transmission. So a mobile can transmit on 1, 2, 4 or even 8 timeslots based on the need, achieving a theoretical maximum data rate of 177.2 kbps. Uplink and downlink timeslots can be allocated independently. This means that quality-of-service (QoS) requirements of fixed packet data networks can be accommodated. GPRS networks support applications based on standard data protocols like IP and X.25.

GPRS networks are backward compatible with GSM networks. They are realized by adding two new nodes to the GSM network. The Serving GPRS Service Node (SGSN) keeps track of individual mobile phones and performs security functions and access control. The Gateway GPRS Service Node (GGSN) provides interworking with external packet-switched networks.

Another technology called Enhanced Data rates for GSM Evolution (EDGE) is poised to increase network speeds, especially when used in conjunction with GPRS. EDGE uses a new modulation scheme called 8PSK (8-phase shift keying) which allows high rates of up to 48 kbps over the air. A GPRS-EDGE network can offer a theoretical maximum of 384 kbps to the end user. EDGE requires an equipment upgrade in existing networks to support EDGE transceivers.

The future - UMTS
The next generation wireless network is called Universal Mobile Telecommunication System (UMTS). The vision behind this technology is to create a universally accessible network. Unlike today's world, a user from the USA should be able to use her mobile device in Europe with no hardware or software changes. To achieve this goal a standardized air interface using Wideband Code Division Multiple Access (W-CDMA) has been adopted.

In addition to universal access, UMTS gives the GSM/GPRS network a chance to catch up with other developments in telecommunications technology. For example, ATM carriers are used as the network backbone, allowing faster and more flexible data transport. A UMTS network supports various data rates depending on the mobility of the user: a stationary user can get up to 2 Mbps while a fast moving user can get 384 Kbps.

The evolution path of GSM networks is shown in Error! Reference source not found.below. Each arrow represents an alternate evolution path.

Wireless applications make all the difference
Our mobile-savvy tourist Mr. Rao would probably use a GPRS or UMTS network and not even know about it! What matters to him is the kind of applications the underlying network supports. Wireless applications will be the key differentiators for any kind of wireless data technology. The search is on for a "killer" application which will get users hooked on to high bandwidth wireless data.

There have been several attempts to standardize the way applications use the underlying wireless network. The hottest standard today is the Wireless Application Protocol (WAP) which is promoted by the WAP Forum, a consortium of over 200 companies involved in wireless development. This protocol allows server-based data applications to send and receive data over any of the standard wireless bearers (SMS, USSD, GPRS, etc.). Any WAP-compliant device can understand this data.

WAP takes a client server approach. The "thin" client resides on the mobile phone and requires low processing power. Most of the intelligence is in the server which is called a WAP gateway. The client (mobile device) requests the server for information using the Wireless Markup Language (WML), a language derived from HTML. This request is carried on one of the standard bearers and routed by the mobile network to the WAP gateway. The gateway then retrieves the information from an Internet server using HTTP. The information may be received by the gateway in WML or in HTML. In the latter case, the gateway needs to perform a translation to WML. The information is sent to the mobile device using a standard bearer.

With the support of powerful protocols like WAP, a number of applications are possible. E-mail, web access and file transfer applications could run on a wireless device. Calendar services and real-time messaging are natural extensions. Mobile banking and shopping-on-the-move applications are already on the market. The stock market, where time is critical, opens up vast possibilities for wireless data applications.

Corporate Wireless: a testing ground for wireless data
A corporate employee represents a mobile subscriber and high bandwidth data user bundled into one package. It is anticipated that wireless data will find its first and most productive markets in the corporate space.

Corporate or enterprise wireless networks provide wireless access to users within the confines of the company premises. They are small-scale networks and can be thought of as wireless extensions of the corporate EPABX. However they use standard GSM technology so that users can use the same mobile devices within and outside the premises. Many corporate wireless are pre-wired for data because they use IP-backbones.

Most of the big wireless players are looking to get into the corporate wireless space. Cisco's acquisition of Jetcell and Siemens' acquisition of OpusWave are indicators of this trend. InterWave, whose GSM-in-a-box technology sets it apart, is another player in this space.

The TechWatch challenge
Use your imagination! Think of an innovative data application and its usage scenario for wireless networks. Assume that bandwidth is no constraint.