The Role of Microwave Technologies in the Wireless Revolution
Manuel del Castillo and Henry Valenzuela
Orland Park, IL
There is no doubt that we are in the middle of a wireless revolution that has been initiated by current digital mobile standards. This wireless boom has accelerated the information revolution that has been changing our lives at an incredibly rapid pace during the past 20 years and, already, the third generation of mobile telephony is emerging.
January 2002 is the scheduled month for the launch of the Universal Mobile Telecommunications System (UMTS), which offers some impressive features. This system aims to be compatible with the Global System for Mobile communications (GSM) and work just like GSM in environments where high mobility is required such as on roads and highways. UMTS will also offer a new set of features related to wideband services in environments where low mobility is required, such as offices, airports and urban areas. These new features include video conferencing, integrated services digital networks and 2 Mbps data rates. Coverage for large areas with hard-to-reach subscribers also will be much improved through the inclusion of low earth orbit satellites that will provide global coverage both on land and at sea.
Driving Forces of the Wireless Revolution
Currently, there are 250 million mobile subscribers worldwide and the growth rate for new subscribers is two per second. This number is expected to double by 2000 and is fueled by two driving forces: technology and politics.
The technological force is key. The GSM standard has shaken the European market. The attraction of a pan-European system has proven to be very popular and, in fact, of the 68.4 million new mobile subscribers worldwide in 1997, 33 percent were European. The technological developments and enhanced features promised by the third generation of mobile telephones will continue to fuel this astonishing growth.
However, without political decisions, growth of such magnitude cannot be achieved. The liberalisation directives set by the European Union are revolutionising the old monopolies country by country. Base station, switching and transmission manufacturers are taking advantage of the increased demands generated by the new operators in the market and are becoming more profitable than expected initially. Even established operators are benefiting from this new liberalised market situation as they lease lines to incoming operators. The good macroeconomic times in which we are living give the average person more money to spend, and good marketing has made the mobile telephone a communication essential. Currently, 115 operators in 63 countries utilize the GSM standard in the 900, 1800 and 1900 MHz frequency bands.
The Role of Microwave Links
The keys for a new mobile service operator to succeed and gain market share are speed and flexibility. Rapid rollouts of four to six months for countrywide coverage have been witnessed recently and even shorter periods can be expected in the future.
There is definitely no time to build a network infrastructure in the old, traditional way. Time is not available for running cables to the base stations or for installing fibre-optic cable between switches. Everything must be based (at least in the first stage) on leasing lines from current operators and creating a network of microwave radio links. This first stage will be essential when the time comes to judge the success or failure of the operator.
The best option for new operators is to lease lines from established operators. However, the logical tendency is for new operators to use their own means to transport the signal since that is the only way to effectively control the global quality of the system. This methodology means laying some fibre cable, but mainly involves setting up terrestrial microwave radio links.
Terrestrial microwave radio links provide good transmission quality while offering a much shorter delivery time and lower price than a buried cable. Obviously, the capacity is smaller in a radio link than in a fibre-optic cable, but this restriction is not an issue in a mobile operator’s network. Capacities involved in radio links starting in a base stations are 2 Mbps or less and, from a base station concentrator to a switch, the capacity can be 4 x 2 Mbps up to 16 x 2 Mbps (sub-STM1) on rare occasions. (One synchronous transport module (STM1) = 155 Mbps.) Links between switches can be 155 Mbps (STM1).
Reliability is another advantage of radio links over buried cable. In the event of a problem in the transmission path, it is much easier to detect and fix a radio link than a buried cable. For radio links, the problem is isolated to the specific site location where there is relatively easy access. However, if a problem exists in a buried cable, much more time is required to locate the site where the cable is broken (because the break can occur at any point along the cable length), repair the break and restore the link.
Three variables should be considered when choosing a radio link solution for a particular link: frequency, antenna size and capacity. The hop length determines the combination of frequency band and antenna size. Capacity is a function of the radio equipment. The International Telecommunication Union recommends several procedures to estimate the quality (bit error rate) of a radio link using a particular frequency, configuration, terrain condition, radio equipment and antennas. These procedures are usually programmed into a PC, allowing the engineer to work with the variables and build the radio link system that best fits a particular application. The next step is for the operations staff to install the particular system configuration chosen by the engineering staff.
Steps towards Even Greater Flexibility
Radio links were the principal transmission means for many telephone operators up until 10 years ago when fibre optics took the lead. However, radio links remain a good technological solution for three purposes: backing up fibre routes (taking advantage of the radio link’s superior reliability), providing access to difficult sites and providing the transmission means to a site where it is urgently required.
The wireless revolution has given great importance to providing the means of transmission. For an incoming operator who invests heavily in equipment and obtaining the licence to operate, it is of the utmost importance to start making money as soon as possible. The radio links are an ideal tool for building a transmission network in a fast, high quality and cost-effective manner. Suddenly, radio links have changed from serving as the main transmission means (where delivery dates of materials could easily be eight months plus an additional month for installation and commissioning) to the present flexibility and speed of delivery that the market is demanding. All the players in the arena continue to progress towards further improvements.
During the last five years, radio manufacturers have been forced to adapt to shorter delivery times and, in response, have developed simple, tunable and versatile radios. Several manufacturers now offer radios that can change their capacity by simply substituting a plug-in card in the equipment. This change makes the network planner’s job much easier because it allows for flexible stocks of material.
Additionally, the new synchronous digital hierarchy (SDH) technologies used in modern radio links of medium (sub-STM1) and high (STM1) capacities allow the operator to supervise the network efficiently and reconfigure it from a computer located in a control centre. The third generation of mobile telephones presumably will require additional capacity and more control of the network by its operators. The mobile telephone will be able to operate in a simple, narrowband mode for transmitting and receiving a voice conversation or in a wideband mode if, for example, the user wants to establish a videoconference or high speed data transmission. During the time the subscriber is using the videoconference service, a higher capacity must be assigned by the network to the mobile telephone. Flexibility and intelligence of the network, efficient supervision and easy rerouting of traffic in the event of a problem are all essential features, and SDH technology radio is prepared to provide them.
Installation companies also have changed the way they work and currently are installing and commissioning radio links in a couple of days (or a maximum of five days when large antennas are involved). Antenna manufacturers have also had to adapt their production lines to allow for higher efficiency and shorter delivery times, and are contributing to this rush with the introduction of new products that are more suitable for this mass market.
Integrating antenna and radio equipment in a single block is an example of new products that allow much quicker and more cost-effective installation of the radio link. Another innovative development is the introduction of new, low profile antennas that satisfy the increasing demand for low environmental impact. Finally, new antennas with improved electrical characteristics help the operators to double their capacity by using both vertical and horizontal polarisations to adapt their network to the higher capacity requirements of the third generation of mobile telephones without consuming more radio channels.
Mobile telephones are only the most visible part of the wireless revolution. People also may remark on the base station towers, but many of them are not aware of the necessary communication network that lies behind it all, a high percentage of which is built on microwave radio links. The role of microwave technologies in the current wireless revolution is to provide a reliable, fast-to-deploy, high quality, cost-effective, flexible and easy-to-supervise transmission network for mobile operators.