Sami Kiminki Department of Computer Science and Engineering Aalto University, School of Science sami.kiminki@aalto.fi September 22, 2011
Introduction A primer for wireless IoT topics Brief overview on current wireless protocols: LTE, WLAN, Bluetooth These protocols have almost completely disjoint design goals Hence, they differ in design philosophies, capabilities, and implementation complexities 6%
Goals LTE: high-quality data, high spectral efficiency, lots of simultaneous users, long distances WLAN: high local speed, simple, coexistence with other equipment Bluetooth: wireless peripherals 11%
Cell characteristics LTE WLAN Bluetooth Max speed 300/75 Mbps 1 600 Mbps 2 2.1 Mbps 3 Max distance 100 km 100 m 10/100 m Active users >200 / 5 MHz BW dozens few per cell Mobility 500 km/h stationary stationary 1 This is LTE UE category 5. UE category 3 (100 Mbps DL/50 Mbps UL) is probably the typical category for mobile phones. 2 Most 802.11n mobile stations support 300 Mbps DL/150 Mbps UL. 3 Bluetooth HS provides higher speeds 17%
Communication model overview LTE: deterministic data transfers are scheduled by the enodeb (LTE base station) centralized scheduling enables high spectrum efficiency network stack complexity is formidable WLAN: opportunistic, best effort data transfers are sender-initiated, except in power-save mode continuous-time contention-based scheduling network stack has single layer, but requires high-speed processing Bluetooth: deterministic master-slave mode slot-based communications, master/slave slots alternate layered, but layers are simple 22%
Communication in LTE (1/2) Three send-receive modes Frequency-division duplex (FDD) Half-duplex FDD Time-division duplex (TDD) Timing: Frames and subframes Subframe is the time-unit (1ms) Frame is 10 subframes, but has meaning mostly in TDD mode Data is transferred by parallel processes (HARQs) 28%
Communication in LTE (2/2) Data is transferred to users inside resource blocks Resource block is 2-dimensional frequency/time block ÑÒÓÔ ÏÐ Figure: Resource assignment example over time and frequency space Image: Dahlman et al.: Key features of the LTE radio interface. Ericsson Review No. 2, 2008 6❹ 6❹ 33%
LTE Resource Allocation and Signalling Details Figure: LTE air resource allocation in a DL subframe Image: Motorola: Long Term Evolution (LTE): Overview of LTE Air-Interface Technical White Paper. 2007 39%
HARQ processes (FDD mode) 4 ms 4 ms UL p1 data p2 ack p1 data DL p2 data p1 ack 1 ms 4 ms 4 ms Figure: HARQ processes in FDD mode. Note: UL=phone base station, DL=base station phone 44%
TDD Framing frame = 10 ms D S U U U D D D D D subframe 0 1 ms 1 2 3 4 5 6 7 8 9 Figure: TDD frame configuration 3 50%
Timing delay and advance enodeb D S U U U D D UE D S U U U D D Figure: Illustration of reception delay and transmission advance 56%
Other Topics Discontinuous reception (DRX) for power saving Timing advance for distance compensation Doppler compensation for high-velocity terminals MIMO, V-MIMO, and beamforming (spatial techniques) Transmit power / channel quality adjustment Modulation optimization Frequency bands 61%
Communication in WLAN Non-structured, contention-based Conceptually simple transfer protocol Two major modes Ad hoc peer-to-peer communication Infrastructure communication via local access point 67%
Sending data in WLAN The procedure (CSMA/CA) 1. Randomize contention time 2. When clear to send, wait for DIFS delay and start decreasing the contention counter 3. When the contention counter reaches zero, send the frame 4. Wait for acknowledgement-frame Shorter time-delay parameters (e.g., SIFS) for management frames 72%
Receiving data in WLAN The procedure 1. Listen for frames 2. When a unicast frame is received, send ack frame There is also a power-save submode in infrastructure mode that does not require listening all traffic 78%
Communication in Bluetooth Master and at most 7 slaves (piconet) Asynchronous (ACL) and synchronous (SCO) connections Asynchronous connections carry data Synchronous connections carry steady-rate streams, e.g., voice 83%
Bluetooth traffic Figure: Bluetooth traffic example Image: Baracoda: Bluetooth protocol. http://www.baracoda.com/shared_docs/bluetooth_protocol.pdf 89%
Power-saving in Bluetooth Four connection modes for slaves (decreasing power consumption) active: listen every master frame sniff: listen every nth master frame hold: go to sleep for a period park: non-active but listens to broadcast messages. Requires specific negotiation to get unparked There is also Bluetooth Low Energy (BLE). This is separate to the main Bluetooth protocol 94%
Conclusions IoT contains different classes of things Sensors, tags, actuators, controllers, gateways, directories,... LTE, WLAN, and Bluetooth might be suitable for some And these protocols help learning the basic concepts However, they at their basic form are not self-adjusting, self-aware, nor self-organizing Some topics network topologies? coexistence? centralized vs. opportunistic timing? Will we get a unified IoT protocol? 100%