IOT Technologies: Radio Frequency Identification (RFID) NETW 1010 IOT Technologies: Radio Frequency Identification (RFID) Dr. Eng. Tallal Elshabrawy Spring 2019

Radio Frequency Identification Battery Lifetime Years RFID Months BLE IEEE 802.15.4 Communication Range Days Few Meters Tens-Hundreds of Meters Kiliometers

Outline Introduction Physical Layer Medium Access

Frequencies & Reading Ranges Frequency Range Frequencies Passive Read Distance Low Frequencies (LF) 120 - 140 KHz 10 – 20 cm High Frequencies (HF) 13.56 MHz < 1 meter Ultra-High Frequencies (UHF) 868 - 928 MHz <10 meters Microwave 2.45 & 5.8 GHz <30 meters

UHF RFID Systems EPCglobal Gen2 Passive Tags Backscatter Modulation Dynamic Frame Slotted ALOHA (DFSA) Up to 10m Read Distance

Backscatter Modulation Tag Antenna Continuous Wave from Reader (868 -915 MHz) Modulating Signal (Typically 40 Kbps) Backscatter Modulated Signal Tag Transmission States Absorb Reflect

Backscatter Communication in Action Continuous Wave Signal Leakage Signal RFID Reader RFID Tag Backscatter Signal 𝑃 𝑅 ∝ 𝑃 𝑇 × 𝐶 𝑑 𝑛 × 𝐶 𝑑 𝑛 Example of a Practical Backscatter Signal Rx Power at Tag Backscatter Rx Power at Reader

RFID Backscatter FM0 Modulation 1 Binary 1 r,r a,a 1 (r,r) (a,a) 1 1 Binary 0 r,a a,r (r,a) (a,r) 1 Example r: reflect a: absorb

RFID Backscatter FM0 Modelling Received Constellation Point when tag is in absorb state Received Constellation Point when tag is in reflect state Constellation Diagram sine axis Envelope Detection (r) cosine axis r1 (a) After removing leakage signal (r) (a)

Electronic Product Code (EPC) Header - Tag version number EPC Manager - Manufacturer ID Object class - Manufacturer’s product ID Serial Number - Unit ID With 96 bit code, 268 million companies can each categorize 16 million different products where each product category contains up to 687 billion individual units

Dynamic Frame Slotted ALOHA (DFSA) Reading frame started by Query Tag chooses random slot counter [0, 2 𝑄 −1 ] Timeslot starts by Query or QueryRep Each timeslot, the tag decrements its counter by one. Tag sends an RN16 message when slot counter reaches 0 Reader replies with ACK. Tag Sends its unique ID “EPC”.

Tag Random or Pseudo-Random Number Generator (RN16) Tags shall generate 16-bit random or pseudo-random numbers (RN16) Alias Tag ID during DFSA medium access Shorter IDs decrease the probability of collisions during DFSA medium access Once RN16 is Acknowledged by the reader, the tag sends its unique EPC code

DFSA Timeslot Types Empty Successful Collision Reader receives no RN16 messages. Reader can decode received RN16 message. Reader cannot detect received RN16 messages.

DFSA Performance Analysis (1) Probability that 𝑘 tags transmitting in a certain timeslot 𝑃 𝑘 = 𝑁 𝑘 ∗ 1 𝐿 𝑘 ∗ 1− 1 𝐿 𝑁−𝑘 Number of tags Number of tags transmitting their RN16 Frame Length ( 𝐿=2 𝑄 ) Empty Successful Collision 𝑃 𝐸 = 𝑃 0 = 1− 1 𝐿 𝑁 𝑃 𝑆 = 𝑃 1 =𝑁∗ 1 𝐿 ∗ 1− 1 𝐿 𝑁−1 𝑃 𝐶 =1− 𝑃 0 − 𝑃 1

DFSA Performance Analysis (2) Maximize Slot Throughput 𝜂 𝑠 𝜂 𝑠 = 𝑃 𝑆 = 𝑃 1 =𝑁∗ 1 𝐿 ∗ 1− 1 𝐿 𝑁−1 d𝜂 𝑠 d𝐿 =0 ⇒−𝑁∗ 1 𝐿 2 ∗ 1− 1 𝐿 𝑁−1 +𝑁∗ 1 𝐿 ∗ 𝑁−1 ∗ 1− 1 𝐿 𝑁−2 ∗ 1 𝐿 2 =0 ⇒− 1− 1 𝐿 + 1 𝐿 ∗ 𝑁−1 =0 ⇒ 𝑳=𝑵, i.e, The reader sets the frame length to be equal to the number of competing tags

DFSA Performance Analysis (3) Maximum Slot Throughput 𝜂 𝑆 𝜂 𝑆 = 1− 1 𝑁 𝑁−1 For a large Tag population 𝑁−1≈𝑁 𝜂 𝑆 = lim 𝑁→∞ 1− 1 𝑁 𝑁 = 1 𝑒 =0.368 Maximum achievable throughput is 36.8% But How can the reader guess the Tag population to set the proper frame length?

Tag Population Estimation After each inventory round, the reader identifies 𝑁 𝐸 empty slots 𝑁 𝑆 successful slots 𝑁 𝐶 collision slots Number of remaining tags could be estimated as 𝑁≈2 ×𝑁 𝐶 𝑁≈2.39× 𝑁 𝐶 The reader then uses estimated 𝑁 in selecting the frame length for the next inventory round