Continuous ARQ Research Articles

A phase II multicenter evaluation of ARQ 197 monotherapy in patients with relapsed or refractory germ cell tumors (GCTs).

4638 Background: ARQ 197 is a selective, oral, non-ATP-competitive, small-molecule inhibitor of the c-MET receptor tyrosine kinase. Preclinical and phase I data suggested a possible role for c-MET in the pathophysiology of GCTs and a potential clinical benefit from ARQ 197 in GCT patients. Methods: Men (≥ 16 years of age) with relapsed or refractory, histologically confirmed, non-central nervous system GCTs received continuous oral ARQ 197 (360 mg twice daily in 28-day cycles) until progressive disease (PD) or unacceptable toxicity. Responses were assessed every 4 weeks during the first 4 cycles, and every 8 weeks thereafter per RECIST v1.1. The primary endpoint was objective response rate within the first 4 cycles, with study termination for < 2 responses amongst the first 21 patients (Simon 2-stage optimal design). Secondary endpoints included 12-week progression-free survival (PFS), overall survival (OS), and safety. Results: 27 patients (median age, 32 years) were enrolled from 9 sites in the US and Europe from February 2010 to November 2010. 25 had non-seminoma histology. Primary tumor sites included testis in 24, and mediastinum in 3. ECOG performance status was 0 (n = 9) or 1 (n = 18). All patients had received ≥ 2 prior lines of chemotherapy and 19/27 (70%) had received high-dose chemotherapy. Among 25 patients evaluable for efficacy, there were no objective responses and accrual was halted once the 21st patient became evaluable. Best response was stable disease in 7 and PD in 18. Median PFS was 32 days (95% CI = 29, 52) and 12-week PFS rate was 14%. Less than half (n = 12) patients have died. Reported grade 3/4 adverse events considered related to study drug were rare and included grade 3 pneumonia and grade 3 syncope (n = 1, each). Conclusions: ARQ 197 was well tolerated but did not demonstrate activity as a single agent in patients with relapsed/refractory GCTs. Correlative biologic data is pending but may provide insight into the lack of efficacy observed. Rapid accrual to this phase II trial was achieved in this rare patient population through multicenter collaboration. Future collaborative trials of novel targeted agents with sound biologic rationale are warranted in relapsed/refractory GCTs.

Blockage mitigation techniques in satellite communications

This article proposes systematic approaches to minimize severe channel degradation. Detection of channel condition is performed by means of two continuous ARQ NAK counting schemes. Stop-and-wait ARQ non-NAK counting is used for timed complete blockage. A single (31,21,5) code is designed for all the ARQ systems proposed. After the blockage state of a transmission channel is determined, satellite link parameter trade-offs and other specific remedy alternatives are recommended to enhance channel performance. System performance criteria are derived with different Earth station capabilities.

Modelling of a VSAT link physical layer fade countermeasure controlled at the data link layer

A satellite data communication link with fade countermeasures applied at the physical layer, in the form of adaptive modulation and forward error correction coding, will only perform as well as governed by the way in which the inherent system adaptivity is controlled. By considering the controlled quality attribute to be the error-free frame throughput of the link, the place where the control happens has to move from the physical layer to the data link layer. Following earlier research which produced excellent results when the OSI HDLC protocol was simulated, the authors have embarked on the development of a fast executing simulator based on a Markov chain architecture. The basic model has been modified by application of adaptive filtering techniques in the calculation of the state change probability values. This refined the model to perform within 2% of the original simulator in the case of the selective repeat continuous ARQ. The paper presents the development philosophy of the new model and some of the results obtained using both deterministic test fades and propagation fades previously recorded by satellite beacon receivers. The good accuracy of the model, coupled with its computation efficiency, makes it suitable for application in future work where a potentially large number of links would have to be simultaneously considered.

Throughput analysis of buffered continuous ARQ scheme with multiple copy retransmission

In this paper, we provide a quantitative analysis of the effect of improving the throughput characteristics by installation of a sequence control buffer in the receiver applied to the continuous ARQ (go-back-N) scheme, which is a typical method of transmission control in data communication networks, for the case when a simultaneous retransmission of multiple copies is allowed. A known method of improvement of the transmission characteristics is to store the correctly received data blocks in a buffer in cases when error recovery procedures are initiated, although no methods of accurate evaluation under the conditions of a reduced throughput have been proposed. In this paper, the error recovery process is expressed as a two-step hierarchical model. In the analysis model prepared for the purposes of this study, the retransmission cycles repeated for error recovery purposes and retransmission sets corresponding to the continuous error recovery operations are represented in the form of a two-step retransmission diagram. Using this model, we have demonstrated that, based on the 1223-type revised mean-value analysis that allows for the estimation of mean values of the influence between the sets, it is possible to considerably reduce the volume of calculations. Using the proposed method of analysis, it is possible to estimate the actual transmission rate within 2.5% of its absolute value, and the round trip delay with a time-dependent remote control can also be approximated. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(1): 49–58, 2001

Improving performance of multidestination ARQ schemes under high error rate conditions

The throughput efficiencies of a cass of continuous multidestination ARQ schemes are evaluated. The operation of the proposed schemes is simpler than that of the schemes studied previously. Numerical results also show that the optimal proposed scheme offers a better throughput performance than the optimal one investigated previously.

Throughput efficiency of a class of continuous ARQ schemes under markovian error patterns

The independent error model is often adopted to simplify the analysis of ARQ strategies. This assumption, however, is not true for channels where transmission errors occur in bursts. The limiting throughput efficiency of a class of continuous ARQ schemes with repeated transmissions is analysed under Markovian error patterns. The scheme without repeated transmissions, i.e. the classic go-back-N scheme, has been analysed in a previous paper. The results show that the throughput efficiency can be significantly increased by transmitting multiple copies of each data block contiguously to the receiver. The results obtained are also compared under Markovian error patterns with those obtained under the independent error model.

Throughput performance of a set of continuous ARQ strategies for Markov channels

Abstract The throughput efficiency of a set of continuous ARQ strategies for Markov channels is analyzed in this paper based on regenerative theorems. The operation of the investigated ARQ strategies can be described as follows. For each data block, a chunk of n or less copies are transmitted contiguously to the receiver. Whenever a repeat request is received, the transmitter goes back to that data block and retransmits the same data block continuously until an ACK is received. Results show that the throughput efficiency depends heavily on the value of n. Therefore, an optimal value of n can be selected to maximize the throughput efficiency. We also compare the throughput performance of the investigated ARQ strategies for Markov systems and systems under the independent error model. It is found that using the independent error model to describe Markov channels may result in significant deviation.

Performance evaluation of efficient continuous ARQ protocols

Generalized continuous automatic-repeat-request schemes with compound error detection (compound go-back-N, or CGBN) and increased bit interval (IGBN) are presented. In the proposed CGBN scheme, sets of identical copies of each block are continuously transmitted through the forward channel to the receiver where soft error detection is performed in conjunction with the standard hard demodulation algorithm on each received block. In this way, errors can often be corrected without the implementation of an explicit correction procedure. Throughput efficiency is increased by optimization of the soft demodulation algorithm and by derivation of the optimum value of the number of identical copies to be transmitted for each data block. The IGBN scheme achieves performance close to that of the optimized CGBN with no additional implementation complexity over a hard-decision decoder by increasing suitably the bit interval. In comparison to classical and and modified versions of continuous ARQ schemes described in the literature, the CGBN and IGBN schemes also achieve better performance in terms of mean buffer occupancy and waiting times. >

Some continuous multidestination ARQ schemes for high error rate conditions

A class of relatively simple continuous ARQ schemes with repeated transmissions suitable for multidestination communications under high error rate conditions is studied. In real applications, one can optimise the throughput performance by choosing the best scheme along those investigated with respect to the round-trip delay, the number of receivers and the block error probability. Results show that the optimal scheme may offer a far better performance than Morris's scheme for multidestination environments.

Throughput performance of some continuous ARQ schemes with memory

A class of continuous ARQ schemes with memory, where multiple copies of each data block are sent contiguously instead of one single copy, and several copies of the same data block are combined to make a decision at the receiver, is considered. The throughput efficiency analysis is carried out based on the model proposed by Bruneel. Results show that the performance of the investigated ARQ schemes can be considerably improved if the receiver has some memory.

Delay performances of a continuous arq system with copy‐transmissions

AbstractThe characteristics of packet transmission delay in a continuous ARQ (Go‐Back‐N type) system are analyzed here. The copies of each packet stored in the buffer are sent to reduce the delay. The optimum copy size minimizing the delay depends not only on packet error probability and round‐trip propagation delay but also on offered traffic intensity. It is possible to reduce the delay by transmitting many copies and using the residual transmission capacity when offered traffic is light. On the contrary, when offered traffic is heavy, transmission of few copies is preferable in consideration of the number of lost copies for a successful transmission. Finally, considering that packet error probability may be reduced in some practical situations, the relation among packet error probability, propagation delay and traffic density where the optimum copy size changes from 1 to 2 is derived.

Throughput efficiency of some ARQ strategies under Markov error models

In the letter we compute and compare the throughput efficiencies of three continuous ARQ strategies under Markov error models. The three strategies are the classic go-back-N, the Sastry modification, and the Moeneclaey and Bruneel scheme. Results show that Sastry's modification is outperformed by either the classic go-back-N scheme or the Moeneclaey and Bruneel scheme.

Continuous multidestination ARQ schemes for high error-rate channels

The authors consider three relatively simple schemes that can effectively be used for multidestination communications using high error-rate channels. The advantage of the schemes over the widely known multidestination go-back-N scheme becomes more evident as the number of destination stations increases. >

On the Throughput Performance of Some Continuous ARQ Strategies with Repeated Transmissions

The paper considers a class of continuous ARQ strategies, whereby multiple copies of each data block are sent contiguously (instead of one single copy), and whereby the data blocks are delivered at the receiver side in their order of arrival at the transmitter. In order to achieve the best possible throughput efficiency-within this class-an optimum value for the number of copies to be sent is determined, in terms of the block error probability and the propagation delay. It turns out that, depending on these parameters, the optimum scheme is one of the two following alternatives: 1) sending each data block repeatedly until a positive acknowledgment is received for it; 2) sending each block a constant (optimum) number of times. A throughput comparison of the optimum scheme with other related ARQ strategies is given.

Steady-state and transient delay analysis of ARQ protocols

A technique for the performance evaluation of ARQ protocols is presented. General distributions for the packet interarrival times at the transmitter are assumed. Two specific ARQ protocols, the stop-and-wait ARQ and the continuous ARQ are examined in particular. Both the transient and steady-state behaviour are obtained. A simple iterative scheme is proposed for the computation of the delay experienced by the packets and for the packet interdeparture time distribution. The latter result can be applied to the analysis of networks using an ARQ protocol in their datalink control layer. This method is demonstrated for the special case of a network consisting of N nodes connected in tandem. Analytical results are compared with simulation runs and excellent agreement is observed.

Efficient ARQ scheme for high error rate channels

The letter proposes a continuous ARQ scheme, to be used under high error rate conditions. The scheme preserves the ordering of the data blocks and yields a better throughput efficiency—especially for channels with large round-trip delay—than some known comparable schemes, for all block error probabilities larger than 50%.