Minimal maintenance link to support sychronization

#Increasing use of wireless telephones and personal computers has led to a corresponding increase in demand for advanced telecommunication services that were once thought practical only for specialized applications. In the 1980s, wireless voice communication became widely available through cellular telephone networks. Such services were thought at first to be the exclusive province of the businessman because of expected high subscriber costs. The same was also true for access to remotely distributed computer networks, whereby until very recently, only business people and large institutions could afford the necessary computers and wireline access equipment.

#As a result of the widespread availability of affordable new technologies, the general population now increasingly desires to have not only wireline access to networks such as the Internet and private intranets, but also wireless access as well. Wireless technology is particularly useful to users of portable computers, laptop computers, hand-held personal digital assistants and the like who prefer access to such networks without being tethered to a telephone line.

#There still is no widely available satisfactory solution for providing low cost, high speed access to the Internet, private intranets, and other networks using the existing wireless infrastructure. This is most likely an artifact of several unfortunate circumstances. For one, the typical manner of providing high speed data service in the business environment over a wireline network is not readily adaptable to the voice grade service available in most homes or offices. Such standard high speed data services also do not lend themselves well to efficient transmission over standard cellular wireless handsets because wireless networks were originally designed only to provide voice services. As a result, present day digital wireless communication systems are optimized for voice transmissions, although certain schemes such as CDMA do provide some measure of asymmetrical behavior for the accommodation of data transmission. For example, the data rate specified by the Telecommunication Industry Association (TIA) for IS-95 on the forward traffic channel is adjustable in increments from 1.2 kbps up to 9.6 kbps for so-called Rate Set 1, and increments from 1.8 kbps up to 14.4 kbps for Rate Set 2. On the reverse link traffic channel, however, the data rate is fixed at 4.8 kbps.

#The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

#FIG. 1 is a general diagram illustrating a wireless communication system according to the principles of the present invention.

#FIG. 2 is a timing diagram illustrating heartbeat slot and link quality management (LQM) slot timing according to the principles of the present invention.

#FIG. 1 is a diagram of a wireless communication system 100 according to the principles of the present invention. A base station 25 maintains wireless communication links with a plurality of field units 42A, 42B, 42C (collectively, field units 42) as shown. Such wireless links are established based upon assignment of resources on a forward link 70 and a reverse link 65 between the base station 25 and field units 42. Each link 65 or 70 is typically made up of several logical channels 55 or 60.

#System 100 supports wireless communications between interface 50 and network 20. Network 20 is typically a Public Switched Telephone Network (PSTN) or computer network such as the Internet. Interface 50 is preferably coupled to a digital processing device such as a portable computer (not shown), to provide wireless access to network 20.

#In an illustrative embodiment, the forward link channels 60 and reverse link channels 55 are defined in the wireless communication system 100 as Code Division Multiple Access (CDMA) channels. That is, each CDMA channel is preferably defined by encoding data to be transmitted over the channel with an augmented pseudorandom noise (PN) code sequence. The PN coded data is then modulated onto a radio frequency carrier. This enables a receiver to decipher one CDMA channel from another knowing only the particular augmented PN code assigned to that channel. In accordance with the preferred embodiment, each channel preferably occupies a 1.25 MHz band consistent with the IS-95 CDMA standard and is capable of transmitting data at 38.4 kbps.