Yohei FUKUMIZU, Shuji OHNO, Makoto NAGATA, and Kazuo TAKI

IEICE (The Institute of Electronics, Information and Communication Engineers)

IEICE Trans A: Fundamentals, Feb 2006; E89-A: 408 - 415.

摘要：本文提出了一种用于高度防碰撞 RFID系统的通信方法，其结合应用了 TD-CDMA技术、 CRC校验技术、错误重发机制。理论分析证明，错误重发机制能够极大的减小标签碰撞的几率；用理想的信道 (无任何噪声干扰 )进行通信，在帧长度为 400微秒的情况下， 1000个标签其被检测的错误率仅为 2.5 ×10-9 。

TD-SCDMA：时分同步码分多址接入CDMA ： Code-Division Multiple Access，码分多址TDMA ： Time Division Multiple Access，时分多址IDER ： ID error rate ， ID错误检测率PRSG ： pseudo random sequence generator ，伪随机序列发生器LFSR ： linear feedback shift register，线性反馈移位寄存器SNR ： signal/noise ratio，信噪比noisy channels：噪声信道

1. 介绍 (Introduction)In this paper, we report a highly collision resistive RFID system that can recognize up to a thousand transponders in 400 msec, featuring impulse-based modulation, anti-collision, error correction, and re-transmission and the ability to communicate in a noisy background. And then explains the proposed communication protocol that enables multiplexing of more than 1k tags. Finally describes an emulation system for evaluating communication robustness against background channel noise.

 

本文首先介绍了一个高度防碰撞的 RFID系统，其应用脉冲调制机制，防碰撞算法，错误收集，错误重发机制，能够在有噪声的环境中实现 400微秒内无错误的读取 1000个标签。然后解释了这个系统的通讯协议，最后介绍了仿真系统在有噪声背景下的有效性评价。

2. System ArchitectureAn RFID system consists of transponders and a reader as shown in Fig. 1.

一个 RFID系统包括应答机 (transponders)，读卡器，如图一所示：

The proposed sequence of identification between a reader and a transponder is shown in Fig. 2. An overview of the communication sequence is given below:

读卡器和应答机之间的识别过程如图二所示：

(i) The reader transmits a continuous power wave in an interrogation zone.Transponders start to charge their capacitors and turns on communication circuits when they enter the interrogation zone.读卡器在查询区域发射连续的功率波；进入查询区域的应答机接收到功率波，开始为电容充电；(ii) The reader requires synchronization by transmitting a one-cycle wave whose phase is shifted 180◦ against the power wave to signify its timing.Each transponder invokes built-in randomizing mechanisms to choose a channel after the synchronization. 读卡器通过发射一个周期的反相波进行同步化处理；应答机则随机的选择一条信道；(iii) Transponders then start to transmit their ID stored in their ROM. After all ID bits are transmitted, the transponder subsequently transmits a CRC error checking code. The reader receives a series of transmitted bits. 应答机发送它们的 ID号，之后再发送 CRC校验码；读卡器接收应答器传送过来的信号；(iv)The reader extracts a CRC code from the series of bits and checks the data’s validity. The verified data is then stored in a memory of a computer.读卡器校验 CRC码，如果确认无误就接收并把它们存储在电脑上；(v) Re-transmission: Repeat (ii)–(iv). 重复 (ii)–(iv)这几个过程，不断循环；

Figure 3 depicts the relationship of waveforms in which (a) shows communication in an ideal noiseless channel and (b) shows it in an actual noisy channel. As the graphs indicate, there are four main factors that lower the quality of communication.应答机和读卡器在理想信道和有噪声的信道中通信，其波形是有差异的，如图三所示 :

There are four reasons about the amplitude of a power transmission wave varies.

1)Variance of power transmission level.

2)Timing jitter caused by the power variance of (1).

3)Variance of modulation output voltage.

4)Voltage suppression of synchronization notification.

传输信号时，波形改变主要有四个原因：1)传输功率的不稳定性；2)由于传输功率的不稳定性导致的波形经过零点时其 振幅发生抖动；3)调制模块输出电压的不稳定性；4)电压的减小抑制了同步化操作；

3. Proposed RFID Communication Scheme3.1 Anti-Collision Mechanism for Multiplexed Communication本文提出的结合 CDMA 和 TDMA优点的 TD-CDMA技术，它能

减短扩频编码的长度，其帧结构如图四所示：

3.2 Re-Transmission and Error-CorrectionTherefore, the transponder repeats transmission of ID information as long as the power is provided. Channel selection is randomized in each re-transmission. Finally, a reader can receive ID information with small collision probability.

当发生碰撞时未能被成功识别的应答器都会重新随机的选择信道，然后重传数据。The proposed system uses the cyclic redundancy check (CRC) procedure, since it gives a reliable checksum and it is easy to actualize its encoder in a piece of hardware.

同时通过发送 CRC校验码，可以比较准确的检验数据的正确性。

4. Emulation System for RFID Multiplexed CommunicationEmulator Architecture shown in Fig. 5 and Fig. 6

仿真系统结构和实物如图五，图六所示，图九为高斯噪声发生器

仿真系统包括两部分：读卡器和应答机，如图七，图八所示；

5. Results5.1 Channel Collision使用 TDMA信道，其 ID错误检测率如图十所示：

从图十可以看出实际的仿真结果和理论计算有点出入，其原因是伪随机序列发生器 (PRSG)使用线性反馈移位寄存器 (LFSR)分配信道时并不是完全真正随机的。

5.2 Noise versus ThresholdFigure 11 shows the relationship between the IDER and the signal/noise ratio (SNR) 。 From the results shown in Fig. 11, it is clear that the IDER can be reduced when thresholds are lowered.ID错误识别率和信噪比之间的关系如图十一所示：从图中我们可以看出当读卡器的阈值电压比较低的时候， ID错误识别率将比较低。

6. ConclusionThese investigations have proved the feasibility of the communication scheme for more than 1k simultaneous recognitions of RFID.

这些试验结果表明，本文提出的通信方法可以识别超过 1000个应答器。