专业英语考试复习总结.doc

1.1 Electronic communication can be summarized as the transmission , reception , and processing of information between two or more locations using electronic circuits . 电子通信就是利用电路在两地或多地之间进行信息的发送、接收和处理。 1.2 Regardless of the particular application, all communications systems involve three main subsystems: the transmitter, the channel, and the receiver. 无论何种具体应用，通信系统都包括三个主要的子系统：发送机、信道和接收机。 1.4 The bandwidth of a communications channel must be large (wide) enough to pass all significant information frequencies. In other word, the bandwidth of the communications channel must be equal to or greater than the bandwidth of information. For example, voice frequencies contain signals between 300Hz and 3000Hz. Therefore, a voice-frequency channel must have a bandwidth equal to or greater than 2700Hz. 信道的带宽必须足够大(宽),以便所有重要的信息频率都能通过。换句话说,信道的带宽必须等于或大于信息的带宽。例如,话音频率包含300Hz到3000Hz的信号。因此,话音频率的信道必须具有等于或大于2700Hz的带宽。 Information capacity is a measure of how much information can be transferred through a communications system in a given period of time 信息容量是在给定时间内,能通过通信系统传送多少信息的量度。 2.3 Suppose, for example, the communications agree to use even parity ; then the parity bit will be a 0 when the number of 1s in the data bit is even and a 1 when it is odd. Hence, if a single bit in a byte is received in error and thereby violates the even parity rule, it can be detected and then corrected through retransmission. 假设，例如，通信同意使用奇偶校验位；然后将在数据位的1的数目甚至和1时，奇怪的是0。因此，如果在一个字节一个单点接收误差，从而违反奇偶校验规则，它可以检测并更正通过重传。 Basically, there are two forms of data compression:(Lossless compression operates by removing the redundant information contained in the data of interest. The compression is said to be lossless because it is completely reversible in that the original data can be reconstructed exactly. Lossless compression is also referred to as data compaction.(Lossy compression involves the loss of information in a controlled manner; the compression may therefore not be completely reversible. Lossy compression is, how