2. FSK Power Optimization

2.1 Introduction

FSK (Frequency Shift Keying) Sub-GHz communication in Amazon Sidewalk provides long-range connectivity with optimized power consumption. This chapter details power optimization techniques specific to FSK links.

2.2 Device Profile Optimization

2.2.1 Profile 1 vs Profile 2

Choose the appropriate profile based on power requirements:

2.2.1.1 Profile 1 (Fixed Configuration)

// Profile 1 - Fixed configuration with infinite RX windows
struct sid_device_profile profile1 = {
    .unicast_params = {
        .device_profile_id = SID_LINK2_PROFILE_1,
        .rx_window_count = SID_RX_WINDOW_CNT_INFINITE,
        .beacon_interval_unit = SID_LINK2_BEACON_INTERVAL_UNIT_1,
        .wakeup_type = SID_TX_AND_RX_WAKEUP,
        .l2_rx_duration_sec = 0  // Infinite for Profile 1
    }
};

sid_error_t err = sid_option(handle, SID_OPTION_900MHZ_SET_DEVICE_PROFILE,
                            &profile1, sizeof(profile1));

Power Characteristics:

• Fixed configuration with infinite RX windows
• Always reachable for downlink messages
• Higher power consumption due to continuous listening
• Limited configurability

2.2.1.2 Profile 2 (Configurable for Power Optimization)

// Profile 2 - All configurable parameters for power optimization
struct sid_device_profile profile2 = {
    .unicast_params = {
        .device_profile_id = SID_LINK2_PROFILE_2,
        .rx_window_count = SID_RX_WINDOW_CNT_INFINITE,  // Fixed for FSK
        .beacon_interval_unit = SID_LINK2_BEACON_INTERVAL_UNIT_2,  // 1, 2, or 3
        .unicast_window_interval.sync_rx_interval_ms = 315,  // 63-5040ms
        .wakeup_type = SID_TX_AND_RX_WAKEUP,  // TX_ONLY, RX_ONLY, TX_AND_RX
        .l2_rx_duration_sec = 3600  // 0 to 65535 seconds
    }
};

sid_error_t err = sid_option(handle, SID_OPTION_900MHZ_SET_DEVICE_PROFILE,
                            &profile2, sizeof(profile2));

Profile 2 Configurable Parameters:

• : 1 (10.08s), 2 (20.16s), 3 (30.24s)
• : 63, 315, 630, 945, 2520, 3150, 5040ms
• : SID_TX_ONLY_WAKEUP, SID_RX_ONLY_WAKEUP, SID_TX_AND_RX_WAKEUP
• : 0 (no downlink) to 65535 seconds

2.3 Beacon Synchronization Optimization

2.3.1 Beacon Interval Configuration

Configure beacon intervals for power efficiency:

• : 10.08s (shortest interval)
• : 20.16s (balanced)
• : 30.24s (least frequent)

2.4 RX Window Optimization

2.4.1 RX Duration Configuration

Profile 2 allows configurable L2 RX duration for power optimization:

// Profile 2 RX duration configuration for power optimization
void configure_profile2_rx_duration(enum application_type app_type) {
    struct sid_device_profile profile = {
        .unicast_params = {
            .device_profile_id = SID_LINK2_PROFILE_2,
            .rx_window_count = SID_RX_WINDOW_CNT_INFINITE,  // Fixed for FSK
            .wakeup_type = SID_TX_AND_RX_WAKEUP
        }
    };

    switch(app_type) {
        case SENSOR_ONLY:
            profile.unicast_params.l2_rx_duration_sec = 0;  // No downlink listening
            break;
        case STATUS_REPORTER:
            profile.unicast_params.l2_rx_duration_sec = 300;  // 5 minutes
            break;
        case INTERACTIVE_DEVICE:
            profile.unicast_params.l2_rx_duration_sec = 3600;  // 1 hour
            break;
        case ALWAYS_REACHABLE:
            profile.unicast_params.l2_rx_duration_sec = 0;  // Infinite (same as Profile 1)
            break;
    }

    sid_option(handle, SID_OPTION_900MHZ_SET_DEVICE_PROFILE,
               &profile, sizeof(profile));
}

2.4.2 RX Window Separation

Optimize RX window separation for Profile 2:

• : Highest responsiveness, highest power
• : Balanced responsiveness and power
• : Lower responsiveness, better power
• : Lowest responsiveness, best power

2.5 FSK Transmit Power Control (TPC)

Amazon Sidewalk does include FSK TPC algorithm that dynamically manages transmit power between Gateway (GW) and End Point (EP) devices by utilizing RSSI and SNR measurements to optimize power consumption while maintaining reliable communication.

How It Works:

• EP sends uplink message using current power level
• Gateway measures RSSI/SNR and calculates optimal power adjustment
• Gateway provides power adjustment feedback via ACK messages
• EP maintains a Channel-Power Mapping Table for 69 channels and adjusts transmit power accordingly

Key Features:

• Dynamic power adjustment range: -20 dBm to +20 dBm
• Channel-specific power mapping for optimal performance
• Quick response to changing link quality conditions
• Configurable SNR thresholds based on data rates

Benefits:

• Optimizes power consumption while maintaining reliable communication
• Adapts to real-time RF conditions
• Channel-specific power optimization

Note: This feature requires enabling application layer acknowledgment (AWS IoT) for optimal operation.

2.5.1 FSK TPC Testing Results

The FSK TPC feature was evaluated under different environmental conditions to assess its power optimization performance. Testing scenarios included interference-free environments, weak interference (4 additional 0 dBm endpoints), strong interference (4 additional 20 dBm endpoints), and various attenuation levels.

Test Environment Configurations:

• Interference-free: Single Endpoint (EN) communicating with single Gateway (GW)
• Weak interference: Single EN with connected GW, plus 4 additional 0 dBm EN transmitting
• Strong interference: Single EN with connected GW, plus 4 additional 20 dBm EN transmitting
• Attenuation: Testing TPC performance with different attenuation levels between EN and GW

TPC Performance Results:

FSK TPC Power Consumption Results

Key Findings:

• : Up to 71.40% when both EN and GW support TPC in interference-free environments
• : TPC maintains 42% power reduction even under strong interference conditions
• : Best results achieved with EN TPC Off and GW TPC On in interference-free scenarios
• : Weak interference significantly reduces TPC effectiveness (8.53% reduction with EN TPC On)
• : TPC provides reliable power savings across different interference scenarios

Implementation Recommendations:

• Consider EN TPC configuration based on expected interference levels
• Monitor interference conditions to optimize TPC settings
• Expect significant power savings (40-70%) in typical deployment scenarios