Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1998-12-22
2002-03-26
Kincaid, Lester G. (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S266000, C455S303000, C455S313000
Reexamination Certificate
active
06363262
ABSTRACT:
FIELD OF THE INVENTION
This invention relates, in general, to a communication device having a wideband receiver capability and an operating method therefor, and is particularly, but not exclusively, applicable to a communication system operating a universal frequency re-use pattern, such as deployed in a code division multiple access (CDMA) environment, in which the use of such a wideband receiver is required to recover broadband signals from a selection of available spectral bands.
SUMMARY OF THE PRIOR ART
Radio frequency (RF) communication systems offer an effective mechanism for supporting data and voice communications. Indeed, cellular RF systems can be quickly deployed to cover large geographic areas, with subscribers to the cellular service merely requiring a handset (or RF modem) to obtain access to the cellular network. This is in stark contrast with conventional wire-line communication systems that necessarily require individual line connections (in the form of twisted pairs or optical fibres) to be made to each subscriber terminal. In fact, the cost of deploying a RF-based cellular service is relatively inexpensive to terms of both time and cost when compared against a wireline system having a similar service capability.
The desirability of implementing RF communication systems is, however, tempered by the limited radio frequency spectrum that is available to support such services. Indeed, commercial cellular services, for example, do not have a uniform spectral frequency allocation on a global basis, with different countries assigning different spectral bands to the same form of service. Furthermore, commercial RF services, generally, are assigned frequency bands that are slotted in between military frequency systems, reserved frequency bands allocated for emergency services and other stellar, commercial or scientific frequency bands. Furthermore, in relation to the assignment of frequencies, national regulatory bodies (such as the Federal Communication Commission (FCC)) allocate radio frequency bandwidth for particular communication services. Indeed with respect to this allocation of frequency, the regulatory authority may not necessarily allocate a single block of spectrum to a particular service, but instead may assign discrete, smaller blocks of spectrum. Indeed, the smaller blocks of spectrum can be supplied from a combination of previously unused spectrum and now system-defunct spectrum that no longer supports a particular form of radio communication, e.g. low RF military application. Consequently, a supplier of infrastructure equipment, particularly, must provision for the subsequent release of radio spectrum for the stipulated communication protocol, e.g. a CDMA modulation scheme.
Consequently, cellular equipment manufacturers, generally, must necessary design systems and handsets that can be adapted (after initial deployment) to support new frequency bands subsequently made available to a network operator, while also having to manufacture equipment that operates at different frequencies. In this latter respect, a change in the operating frequency does not necessarily require a simple alteration in the receiver front end, but instead may require re-design of a significant portion of a transceiver to order to produce an operational unit at a different frequency. Clearly, any re-design of equipment is both costly and time consuming for the manufacturer.
Nevertheless, the popularity of RF-based systems is placing ever-increasing demands on the limited radio spectrum, and in this respect cellular communication systems have been developed that attempt to optimise that available bandwidth. For example, the global system for mobile (GSM) cellular communication systems operates a time division multiplexed scheme in which a carrier frequency supports a number of time multiplexed communication channels, with each carrier frequency framed into time slots.
Unfortunately, time division multiple access (and, for that matter, frequency division multiple (FDM) schemes, generally) necessarily operate frequency re-use patterns within the cellular system. More specifically, cells in the system have frequency carriers assigned to them (usually) on a permanent basis and in a way that interference between frequency carriers on an adjacent channel and co-channel basis is minimised. In other words, re-use of a first carrier frequency may be prohibited in adjacent cells so as to improve the radio environment by limiting potential interference (caused by a substantially identical frequency carriers corrupting the integrity of each others data).
In an attempt to further enhance capacity of time division multiplexed (TDM) systems, re-use patterns may, in fact, be on a sector basis, with each cell containing typically three or more sectors. In this way, lower power transmissions may be used, whereby interference from a particular frequency carrier is reduced (as a consequence of the effective transmission distances of these lower power signals) and carrier re-use hence increased. Furthermore, present TDM systems can operate frequency patterns that employ the underlay of microcells (or picocells) beneath macrocells. Again, such a system increases capacity, but still suffers from co-channel and adjacent channel interference.
A more efficient cellular communication scheme is the nineteen-hundred MegaHertz (MHz) personal communication system (PCS) operated in North America, which scheme operates a code division multiple access (CDMA) technique.
In contrast to TDM-based cellular systems, a CDMA system has a universal frequency re-use that allows frequencies to be used across the entire network, i.e. there is a frequency re-use of one. Such CDMA systems operate by virtue of the fact that a single carrier frequency supports a number of communication resources that are structured from discrete, coded sequences. More specifically, each channel is comprised from a unique coded sequence of “chips” that are selected from a relatively long pseudo-random spreading sequence (typically many millions of bits in length). A communication device therefore has access to an information-bearing channel by virtue of a communication device having particular and detailed knowledge of a specific code that identifies the specific bits used by the information-bearing channel. More particularly, information (such as voice or data) is spread across many chips of the spreading sequence on a unique basis, with a processing gain of the system determined by the number of chips required to construct a single data bit. In this way, less than one bit of information is transmitted per chip.
CDMA systems therefore inherently operate in an interference environment because many channels utilise the same carrier frequency, with individual channels merely differing from one another in terms of their uniquely defined coded sequences. However, CDMA systems become statistically efficient for large populations of users, and therefore present an attractive and more efficient alternative to FDM-based systems.
CDMA systems must therefore necessarily impose and retain strict power controls on all transmissions, with this being particularly important in relation to transmissions from mobile communication devices. Unfortunately, CDMA systems are prone to operational instability in the face of “rogue mobiles” in close proximity to base station transceivers and which rogues mobiles transmit at high power levels. As will now be appreciated, high-powered transmissions from the rogue mobile will swamp the universal frequency carrier and therefore corrupt information bearing chips, with this effect known as the “near-far” problem. Indeed, the near-far problem can ripple-through and potentially unbalance the whole CDMA system to an extent where system-wide failure can result; this is clearly catastrophic for a network operator and must be avoided at all costs.
Other mechanisms that allow the radio spectrum to be utilised more efficiently include that concept of using lower bit-rate voice coders (termed “vo-coders”). Unfortunately, while increasi
Kincaid Lester G.
Lee Mann Smith McWilliams Sweeney & Ohlson
Northern Telecom Limited
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