Land Mobile Communications: Cellular Radio, Paging, and Personal Communication Services

Abstract

Land mobile communications dates back to the 1920s; and it has served well, although comparatively inconspicuously, ever since. In that period, the majority of land mobile systems were used for public safety and vehicle dispatching. Only since the mid‐1980s have land mobile systems started to really take their place in the business community. Cellular radio began the explosive march. The kickoff event was a description of an analog FM system called AMPS (advanced mobile phone system) in a 1979 issue of Bell System Technical Journal. Since then, it seems, the number of cellular radio subscribers doubles every year. Paging has seen equivalent acceptance as universal worldwide. PCS (personal communication services) is currently experiencing eruptive emergence. From our perspective, it seems no more than an outgrowth of the cellular radio concept with shorter ranges and lower power. Both face the problem of building penetration. Some cordless telephone systems are truly evolving into the PCS category, such as the DECT (digital European cordless telephone). Another application of PCS with great promise is the wireless local loop (WLL). In this case, instead of connecting the local serving exchange to the subscriber by wire pair, a radio technique is employed. Such systems can be implemented very rapidly at about half the cost of an equivalent wired system. Where competition is permitted in the local serving area, it would be advisable to avoid the additional wired approach and use radio instead. [ Note: The current popular press uses the word wireless . The term was widely used in Great Britain. In North America its connotation is slightly different. All of the applications discussed in this chapter would be called wireless. However, we will use the traditional, more meaningful term: radio .] Cellular radio is chronically short of bandwidth and has turned to using many different means to conserve bandwidth (i.e., achieve more users per unit of bandwidth). PCS, although assigned four times as much bandwidth, will eventually suffer the same demise. A drawback of present cellular radio is the lack of a universal standard. Europe is further along in this regard with its GSM, which is digital, uses a TDMA access technique, and is fairly bandwidth conservative. It is even making inroads in North America. Currently, North America has two different TDMA systems, two CDMA systems, and two analog systems (i.e., AMPS and N‐AMPS). Multipath reception has the potential to corrupt performance in both PCS and digital cellular radio. Its corruptive effects increase as bit rate increases. These harmful effects can be mitigated by using direct sequence spread spectrum transmission along with digital signal processing.

Liver, Biliary Tract and Pancreas

“…(50) Freeman (62) has connected the gallbladder directly to the urinary bladder by means of a plastic conduit. With all these methods, the bile i s diverted into the urinary system after ligation of the common duct.…”

Implications of Regional Transmission Organization Design for Renewable Energy Technologies

“…There is no practical difference between bidding unavailable and bidding as a price taker, except constantly bidding zero into PJM may trigger a review by the PJM market monitor. To avoid this, PJM has instructed some of the intermittent renewable energy generators to bid unavailable into PJM (Freeman 2002). As with the price taker option, the intermittent generator cannot set the prevailing market price in PJM-it can only take the prevailing market price.…”

“…PJM has 199 members as of April 2002(PJM 2002b. To become a member, an entity must comply with the PJM operating agreement and be a transmission owner within the PJM control area or an eligible customer under the PJM tariff; a generation owner, supplier, electric distributor, or end-user customer; or an entity that will buy, sell or transmit electric power in or through the PJM.…”

“…Intermittent renewable generators that bid unavailable or bid into PJM as a price taker will not have to balance their real-time deliveries with their advance schedules, but will have to pay real-time operating reserve costs if the energy that is delivered exceeds 5 MW. Real-time operating reserve costs generally cost about $0.50/MWh over an entire year (Freeman 2002).…”

“…The wind plants are designated as unavailable and output from the two wind projects is sold into the PJM real-time energy market, while "green tags" representing the environmental attributes of wind energy are sold to customers (Freeman 2002). Wind energy currently is a very small percentage of available resources in PJM, but it is likely that PJM will want wind energy generators to use a different market strategy than being unavailable if a significant amount of wind becomes operational in PJM.…”