Some asymptotic properties of the entropy of a stationary ergodicdata source with applications to data compression

Theorems concerning the entropy of a stationary ergodic information source are derived and used to obtain insight into the workings of certain data-compression coding schemes, in particular the Lempel-Siv data compression algorithm     

Information-theoretic considerations for symmetric, cellular,multiple-access fading channels. II

For pt.I see ibid., vol.43, no.6, p.1877-94 (1997). A simple idealized linear (and planar) uplink, cellular, multiple-access communication model, where only adjacent cell interference is present and all signals may experience fading is considered. Shannon theoretic arguments are invoked to gain insight into the implications on performance of the main system parameters and multiple-access techniques. The model treated in Part I (Shamai, 1997) is extended here to account for cell-site receivers that may process also the received signal at an adjacent cell site, compromising thus between the advantage of incorporating additional information from other cell sites on one hand and the associated excess processing complexity on the other. Various settings which include fading, time-division multiple access (TDMA), wideband (WB), and (optimized) fractional inter-cell time sharing (ICTS) protocols are investigated and compared. In this case and for the WB approach and a large number of users per cell it is found, surprisingly, that fading may enhance performance in terms of Shannon theoretic achievable rates. The linear model is extended to account for general linear and planar configurations. The effect of a random number of users per cell is investigated and it is demonstrated that randomization is beneficial. Certain aspects of diversity as well as some features of TDMA and orthogonal code-division multiple access (CDMA) techniques in the presence of fading are studied in an isolated cell scenario     

Information rates for a discrete-time Gaussian channel withintersymbol interference and stationary inputs

Bounds are presented on I_i.i.d.-the achievable information rate for a discrete Gaussian Channel with intersymbol interference (ISI) present and i.i.d. channel input symbols governed by an arbitrary predetermined distribution p_x(x). The lower and upper bounds on I _i.i.d. and I are formulated. The bounds on I_i.i.d. are calculated for independent equiprobably binary channel symbols and for causal channels with ISI memory of degree one and two. The bounds on I_i.i.d. are compared to the approximated (by Monte Carlo methods) known value of I_i.i.d. and their tightness is considered. An application of the new lower bound on I_i.i.d. yields an improvement on previously reported lower bounds for the capacity of the continuous-time strictly bandlimited (or bandpass) Gaussian channel with either peak or simultaneously peak power and bandlimiting constraints imposed on the channel's input waveform     

Information theoretic considerations for cellular mobile radio

We present some information-theoretic considerations used to determine upper bounds on the information rates that can be reliably transmitted over a two-ray propagation path mobile radio channel model, operating in a time division multiplex access (TDMA) regime, under given decoding delay constraints. The sense in which reliability is measured is addressed, and in the interesting eases where the decoding delay constraint plays a significant role, the maximal achievable rate (capacity), is specified in terms of capacity versus outage. In this case, no coding capacity in the strict Shannon sense exists. Simple schemes for time and space diversity are examined, and their potential benefits are illuminated from an information-theoretic stand point. In our presentation, we chose to specialize to the TDMA protocol for the sake of clarity and convenience. Our main arguments and results extend directly to certain variants of other multiple access protocols such as code division multiple access (CDMA) and frequency division multiple access (FDMA), provided that no fast feedback from the receiver to the transmitter is available     

A recurrence theorem for dependent processes with applications todata compression

In an earlier work, Wyner and Ziv (see ibid., vol.35, no.6, p.1250-8, 1989) proved theorems on recurrence times for strings in a random sequence, and applied these theorems to data compression and the Lempel-Ziv algorithm. It is shown that one of these theorems holds under an essentially weaker hypothesis. The new proof is considerably simpler than the original     

Improved success of living unrelated renal transplantation with cyclosporine immunosuppression

Kidney transplantation with a living unrelated donor was performed in 13 patients. The donors comprised 10 spouses, 2 brothers-in-law and 1 stranger. All donor-recipient pairs were red blood cell compatible with a negative T cell crossmatch. Five patients underwent transplantation before 1984 without cyclosporine immunosuppression; the 1-year patient and graft survival rates in this group were 40% and 20%, respectively. Eight patients have undergone transplantation since 1985 with cyclosporine immunosuppression. The 1-year patient and graft survival rates in this group were 100% and 88%, respectively (p = 0.03). Currently, 6 patients in the latter group have a well functioning graft with serum creatinine levels of 1.2 to 2.0 mg./dl. (mean 1.5 mg./dl.) and with followup of 1 to 6 years (mean 2.9 years). Excellent graft survival results can now be achieved with living unrelated donors and their expanded use can provide an important additional source of organs for transplantation.     

ASSESSMENT OF THE NATIONAL BUREAU OF STANDARDS PROPOSED FEDERAL DATA ENCRYPTION STANDARD

The National Bureau of Standards (NBS) has implemented a Data Encryption Standard (DES), describing an encryption procedure to be used by Federal agencies and others to protect data against unauthorized access. This procedure encrypts 64-bit data sequences using a 56-bit key. Diffie, Hellman and others have objected that a 56-bit key may be inadequate to resist a brute force attack using a special purpose computer costing about $20 million. Others have estimated ten times that much. Whichever figure is correct, there is little safety margin in a 56-bit key.     

The sliding-window Lempel-Ziv algorithm is asymptotically optimal

The sliding-window version of the Lempel-Ziv data-compression algorithm (sometimes called LZ '77) has been thrust into prominence recently. A version of this algorithm is used in the highly successful “Stacker” program for personal computers. If is also incorporated into Microsoft's new MS-DOS-6. Although other versions of the Lempel-Ziv algorithm are known to he optimal in the sense that they compress a data source to its entropy, optimality in this sense has never been demonstrated for this version. In this self-contained paper, we will describe the algorithm, and show that as the “window size,“ a quantity which is related to the memory and complexity of the procedure, goes to infinity, the compression rate approaches the source entropy. The proof is surprisingly general, applying to all finite-alphabet stationary ergodic sources     

Capacity and error exponent for the direct detection photonchannel. I

The capacity and the lower bound on the error exponent of a direct detection optical channel are derived. The channel input in a T-second interval is a waveform satisfying certain peak and average power constraints for the optical signal. The channel output is a Poisson process with a given intensity parameter; the intensity parameter takes account of the dark-current signal component. An explicit construction for an exponentially optimum family of codes is also presented