tailieunhanh - The Cellular Connection 1 phần 2

Hệ thống thông tin liên lạc di động đầu tiên bắt đầu vào năm 1921 khi Cục Cảnh sát Detroit cài đặt radio hai chiều trong xe hơi của nó. Các thiết bị cồng kềnh, khó khăn, và một cống trên pin ô tô, nhưng nó đã chứng minh giá trị của nó. Ngay sau đó cảnh sát và sở cứu hỏa trong cả nước đã được cài đặt thiết bị vô tuyến hai chiều trong đội tàu của mình. | The Cellular Connection A Guide to Cellular Telephones Fourth Edition. Robert A. Steuernagel Copyright 2000 John Wiley Sons Inc. ISBNs 0-471-31652-0 Paper 0-471-20340-8 Electronic 1 AN INTRODUCTION TO CELLULAR PHONE SYSTEMS The first mobile communications system began in 1921 when the Detroit Police Department installed two-way radios in its cars. The equipment was bulky awkward and a drain on automobile batteries but it proved its worth. Soon police and fire departments throughout the country were installing two-way radio equipment in their fleets. Eventually someone realized that private individuals could also benefit from being able to talk with the outside world from their cars and the first commercial mobile telephone service was instituted in St. Louis Missouri in 1946. Early mobile phone service was more like using a radio than a phone. You spoke into a microphone or special handset and the voice from the other end of the connection usually came through a loudspeaker. You couldn t dial a call instead the mobile operator at the other end of your radio link established the connection for you. It could take some time before you got through since only a few radio telephone channels were available in any city and you frequently had to wait for a free one. When you finally did get through your conversation was clumsy at best. Because of the nature of the equipment you and the party you were speaking with had to take turns talking pushing a button before you spoke. If you tried to say something while the other party was speaking they wouldn t be able to hear you and you wouldn t be able to interrupt them. You had to wait until they decided that 1 2 AN INTRODUCTION TO CELLULAR PHONE SYSTEMS they had had their say and gave you the go-ahead to speak a very frustrating experience as you can well imagine. Still it was worth putting up with such hardships to be able to accomplish needed business while on the road or just to enjoy the luxury of chatting with friends as .