Leonard N. Schiff

Signal design and system operation of Globalstar versus IS-95 CDMA—similarities and differences

The GlobalstarTM system provides telephone and data services to and from mobile and fixed users in the area between ±70 degrees latitude. Connection between user terminals and the PSTN is established through fixed terrestrial gateways via a constellation of low earth orbiting (LEO) satellites. Globalstar uses an extension of the IS‐95 CDMA standard that is used in terrestrial digital cellular systems. The LEO satellite link is sufficiently different from the terrestrial cellular link that certain departures from IS‐95 were needed both in signal design as well as in system operation. This paper describes some of the similarities and differences of Globalstar air interface versus IS‐95.

System operation for IS-95 terrestrial vs. Globalstar/sup TM/-similarities and differences

The Globalstar/sup TM/ system provides telephone and data services to mobile and fixed users between /spl plusmn/70/spl deg/ latitude. Connections are made from the mobile user to one of a group of fixed terrestrial gateways via a constellation of low Earth orbiting satellites (LEOs). Globalstar uses an extension of the CDMA, IS-95 standard used for cellular systems. The satellite link is sufficiently different from the terrestrial link that certain departures from IS-95 were needed both in signal design and in system operation. This paper describes some ofthe similarities and differences with IS-95.

The asymptotic error probability for transmission of orthogonal signals over the generalized incoherent channel

The probability of error for the transmission of one of M -orthogonal, equally likely, equal-energy signals over the white Gaussian noise channel is known. For large values of T it is shown that this result is asymptotically equivalent to the error probability for the same signal set transmitted over a different channel, termed here the generalized incoherent channel of order v . For v = 2 this channel is identical to the phase incoherent channel. This problem, for larger values of v , also arises in a number of other applications, some of which are given.

Appliqueing IMT-2000 features onto Globalstar

The IMT-2000 process of the ITU is intended to provide standardized ways of providing high data rate and multimedia services to the wireless user. The cdma2000 proposal for a 3rd generation terrestrial standard is a way of providing these services in a backwardly compatible and evolutionary way for the IS-95 user. The Globalstar LEOS MSS system uses waveforms and procedures derived from IS-95. Our purpose in this paper is to show that many of the features of cdma2000 can be appliqued onto the Globalstar system in an evolutionary way that achieves backward compatibility.

High-speed binary data transmission over the additive band-limited Gaussian channel

The transmission of the linear sum of m biphase modulated signals in a time interval T is considered for an additive Gaussian white noise channel of bandwidth W . Previous analyses consider the case where m \leq n \equiv 2WT . In this paper, the probability of error is derived for m > n , a situation which arises when the channel bandwidth is insufficient to support the data rate. Two distinct problems are considered. In the first, termed uncoded transmission, all m signals are independently biphase modulated. It is shown, for this case, that if the channel signal-to-noise ratio increases linearly with n , the error probability can be made to go to zero approximately exponentially in n for any value of m/n . In the second problem, termed ceded transmission, only k of the signals are independently modulated. (The remaining (m - k) signals carry redundant information.) By using a suboptimum receiver, it is shown that for a fixed channel signal-to-noise ratio the error probability goes to 0 exponentially in n if k/n is less than some number C^{\ast} . For high signal-to-noise ratio, C^{\ast} is greater than 1 , a situation which could not occur if m \leq n .