Wednesday, December 19, 2007

Slot Aloha Limit Throughput

EPC Gen2 builds on slot Aloha, which has a crucial nature:
Max Throughput = 1 / e = 36.79%

Simulator generates the result around 34% (above 1000 tags)

Now the concentrates are on:
Reduce Q parameter update frequency: as far as we know, Q parameter decreases as the detection process going. Fluctuating Q causes redundant data in transmission.

Find an out of box method to break the slot Aloha throughput limit.

Friday, December 14, 2007

Slot-count(Q) selection algorithm

Slot-count(Q) selection algorithm is a recommendation algorithm, which is accompanied with EPC Gen2. It seems the protocol doesn't mention in what case to use this algorithm and update Q parameter, so I think this is left to the designer to deal with or even you can have you own Q generating algorithm. This algorithm is not necessary a part of EPC Gen2 protocol.

Thursday, December 13, 2007

EPC Gen2 Pseudo Code

I use Java to implement this algorithm. This can simulate the communication between tags and reader, and statistics can be collected in each cycle or slot.

It is still unclear about when to update tag's Q parameter. This algorithm assumes it updating each collision or some empty cycles.

The performance is mentioned in previous blog entry. Basically, three cycles for identifying one tag.

Wednesday, December 12, 2007

Made the First simulation

Run the first simulation. It seems all good to the simulator, but the result of performance is under my expectation, as most of the time, collision happens.

Crucial Issues:
How frequent to update Q parameter using that official algorithm?
Every queryRep queryAdjust or follow other rule

The rule, or the way to adjust the gap (the C parameter) in each update of Q parameter.

Brief Performance Summary:
Tags Number * 3 = Query Number (20 - 5000 tags)
Three query messages needed to identify one tag

Wednesday, December 05, 2007

Detail in Class 1 and Implement Gen2

Passive Tag Transmission in Class 1:
5.2. Reader-Tag Half-Duplex Communication
As specified in Section 6, the Reader-to-Tag and Tag-to-Reader communication occurs in a half-duplex manner. The Reader initiates communication by modulating a complete command. The Reader then transmits an unmodulated continuous wave (CW) signal. The Tag modulates its reflection of the CW signal (backscatter communication).
5.3. Reader-to-Tag Communication Signals
A Reader may emit no signals at any frequency, may emit a CW signal at a single frequency, or may emit a modulated signal at a single frequency.
5.3.1. Reader-to-Tag Signal Modulation Depth
The Reader communicates with tags using Amplitude Shift Keying (ASK) with a minimum modulation depth of 30% and a maximum modulation depth of 100%. Modulation shape, depth and rate of modulation are variable within the limits described below. Compliant Tags will adjust their timing over a range of modulation rates to lock to reader transmissions automatically during the [CLKSYNC] period of a Reader command.

Have read Class 1 Gen2 specification, draft the pesudo-code framework using Java. Thinking about a whether a discrete simulation is necessary, and the means of performance measurement.

In implement simulation of Gen2, a simplification is made in message transmission, like ACK and Session selection etc., which have no influence in the anti-collision measurement so far.

Session selection deals with Reader-to-Reader collision.
ACK is reliable transmission and for further processing in tag.