In this paper, a slot-averaged SIR model is derived to analyze the performances of 1/N-slotted DS-CDMA packet radio networks. DS-CDMA packet radio networks can be analyzed with channel threshold model, but it is not appropriate for a 1/N-slotted access scheme since the interference level varies slot by slot during a packet transmission time. A packet in a DS-CDMA system will be channel-encoded and interleaved so that an excessive interference of some slots does not result in a corruption of a packet directly. In a 1/N-slotted DS-CDMA packet system, interleaving and channel coding can cope with the excessive interference in some slots. Proposed slot-averaged SIR model reflects this effect and is simple enough to be used in the performance analyses of various packet access control schemes. This paper verifies the slot-averaged SIR model and evaluates the throughputs of 1/N-slotted access schemes using it. This paper also compares the results with those of the conventional channel threshold model. Packet access schemes such as slotted ALOHA, slotted CLSP and slotted CLSP/CC are analyzed. The results show that many different aspects from the results of the previous works can be evaluated and this work will offer more accurate view on the behavior of 1/N-slotted DS-CDMA packet radio networks.

As noncoherent direct sequence code-division multiple-access (DS-CDMA) mobile satellite communications, two typical transmission schemes are compared; one is a quasi-synchronous differential BPSK (QS-DBPSK) where orthogonal signals are used for reducing the multiple access interference and the other is M-ary orthogonal signaling (MOS) scheme where orthogonal signals are used for exploiting more efficient modulation. The performances are evaluated in additive white Gaussian noise (AWGN) and shadowed Rician fading (SRF) channels and the effects of timing misalignments in the QS-DBPSK system and the amount of Doppler shifts of a SRF channel are investigated. The results show that MOS much outperforms QS-DBPSK in the region of low system loading up to about 50% and a precise chip synchronization is required for QS-DBPSK. In a SRF channel, it is also shown that QS-DBPSK much outperforms MOS in a slow fading channel but MOS has a performance gain against the large Doppler shift.

We propose an enhanced packet access scheme for IMT-2000/UMTS random access channel (RACH). In the proposed scheme, 2-level preamble detection threshold and 2-level message transmission power are used to mitigate the power imbalance in RACH. Simulation results demonstrate that the proposed scheme improves the interference characteristics of the conventional RACH and makes wider range of the detection threshold available.